Conformational analysis of 2-oaryl-2-oxo-4,6-dimethyl- and -4-methyl-1,3,2λ5-dioxaphosphorinanes. Spectroscopic, X-ray, and solid-state 13C and 31P studies

Heteroatom Chemistry

Volumn 8, Issue 6, 1997, Pages 509-516

  Eliel, Ernest L ^a   Gordillo, Barbara ^a,b   White, Peter S ^a   Harris, David L ^a  

^a The University of North Carolina at Chapel Hill   (United States)

^b DEPARTAMENTO DE FÍSICA   (Mexico)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0006572904     PISSN: 10427163     EISSN: None     Source Type: Journal    
DOI: 10.1002/(sici)1098-1071(1997)8:6<509::aid-hc9>3.3.co;2-h     Document Type: Article

References (56)

1. B. Gordillo, E. L. Eliel, J. Am. Chem. Soc., 113, 1991, 2172.
2. (a) The free-energy difference between chair and boat conformations of cis-2,5-di-tert-butyl-1,3,2-dioxaphosphorinane-2-one ring was reported to be 1 kcal/mol or less: cf. G. W. Bentrude, K. C. Yee, J. Chem. Soc. Chem. Commun., 1972, 169 and references cited therein. This is in contrast with the difference between boat or twist and chair conformations in 1,3-dioxanes or cyclohexanes that are of the order of 5-6 kcal/mol. (b) Some other heterocycles containing phosphorus-V also prefer twist-boat conformations. U. Engelhardt, A. Simon, Z. Anor. Allg. Chem., 619, 1993, 1177.
3. (a) The free-energy difference between chair and boat conformations of cis-2,5-di-tert-butyl-1,3,2-dioxaphosphorinane-2-one ring was reported to be 1 kcal/mol or less: cf. G. W. Bentrude, K. C. Yee, J. Chem. Soc. Chem. Commun., 1972, 169 and references cited therein. This is in contrast with the difference between boat or twist and chair conformations in 1,3-dioxanes or cyclohexanes that are of the order of 5-6 kcal/mol. (b) Some other heterocycles containing phosphorus-V also prefer twist-boat conformations. U. Engelhardt, A. Simon, Z. Anor. Allg. Chem., 619, 1993, 1177.
4. Reviews of the sterochemical aspects of phosphates can be found in (a) B. E. Maryanoff, R. O. Hutchins, C. A. Maryanoff: in E. L. Eliel, N. L. Allinger (eds): Topics Stereochemistry, vol. 11, p. 187 (1979). (b) M. J. Gallagher: in J. G. Verkade, L. D. Quin (eds): Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis: Organic Compounds and Metal Complexes, VCH Publishers, Inc. Deerfield Beach, FL, (1987) 297. (c) D. G. Gorenstein, R. Rowell, K. Taira: in L. D. Quin, J. G. Verkade (eds): Phosphoms Chemistry, ACS Symposium Series No. 171, American Chemical Society, Washington D.C. (1981) 69.
5. Reviews of the sterochemical aspects of phosphates can be found in (a) B. E. Maryanoff, R. O. Hutchins, C. A. Maryanoff: in E. L. Eliel, N. L. Allinger (eds): Topics Stereochemistry, vol. 11, p. 187 (1979). (b) M. J. Gallagher: in J. G. Verkade, L. D. Quin (eds): Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis: Organic Compounds and Metal Complexes, VCH Publishers, Inc. Deerfield Beach, FL, (1987) 297. (c) D. G. Gorenstein, R. Rowell, K. Taira: in L. D. Quin, J. G. Verkade (eds): Phosphoms Chemistry, ACS Symposium Series No. 171, American Chemical Society, Washington D.C. (1981) 69.
6. Reviews of the sterochemical aspects of phosphates can be found in (a) B. E. Maryanoff, R. O. Hutchins, C. A. Maryanoff: in E. L. Eliel, N. L. Allinger (eds): Topics Stereochemistry, vol. 11, p. 187 (1979). (b) M. J. Gallagher: in J. G. Verkade, L. D. Quin (eds): Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis: Organic Compounds and Metal Complexes, VCH Publishers, Inc. Deerfield Beach, FL, (1987) 297. (c) D. G. Gorenstein, R. Rowell, K. Taira: in L. D. Quin, J. G. Verkade (eds): Phosphoms Chemistry, ACS Symposium Series No. 171, American Chemical Society, Washington D.C. (1981) 69.
7. (a) P. Van Nuffel, C. Van Alsenoy, A. T. H. Lenstra, H. J. Geise, J. Mol. Struct. 125, 1984, 1;
8. (b) D. G. Gorenstein, R. Rowell, J. Am. Chem. Soc., 101, 1979, 4925;
9. (c) D. G. Gorenstein, Chem. Rev., 87, 1987, 1049.
10. (a) J. H. Yu, A. E. Sopchik, A. M. Arif, W. G. Bentrude, J. Org. Chem., 55, 1990, 3444 and references cited therein;
11. (b) A. E. Sopchik, G. S. Bajwa, K. A. Nelson, W. G. Bentrude: in L. D. Quin, J. G. Verkade (eds): Phosphorus Chemistry, ACS Symposium Series No. 171, American Chemical Society, Washington D.C. (1981) 217.
12. K. A. Nelson, W. G. Bentrude, W. N. Setzer, J. P. Hutchinson, J. Am. Chem. Soc., 109, 1987, 4058.
13. Properties and analyses of compound 5a are as described in Ref. [1b].
14. (a) D. G. Gorenstein, R. Rowell, J. Findlay, J. Am. Chem. Soc., 102, 1980, 5077 and references cited therein;
15. (b) J.-P. Majoral, J. Navech, Bull Soc. Chim. Fr., 1971, 1331.
16. -1. This has been attributed to the presence of rotational isomers; cf. J. A. Mosbo, J. G. Verkade, J. Org. Chem., 42, 1977, 1549.
17. Since IR transitions are faster than ring inversions, IR bands for individual ring conformers should be seen; cf. D. W. White, G. K. McEwen, R. D. Bertrand, J. G. Verkade, J. Chem. Soc. (B), 1971, 1454.
18. A 40-100% contribution of twist-boat conformations has been postulated in analogous annelated equatorial phosphate esters. See Ref. [8a] and J. A. Mosbo, Org. Magn. Res., 11, 1978, 281.
19. 5; cf. M. Haemers, R. Ottinger, D. Zimmermann, J. Reisse, Tetrahedron, 29, 1973, 3539. See also Ref. [13a].
20. (a) L. D. Quin: in J. G. Verkade, L. D. Quin, (eds): Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis: Organic Compounds and Metal Complexes, VCH Publishers, Inc., Deerfield Beach, FL(1987) 391.
21. (b) See also Refs. [3a] and [8a].
22. HaHa are somewhat small: W. G. Bentrude, W. N. Setzer: in J. G. Verkade, L. Quin, (eds): Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis: Organic Compounds and Metal Complexes, VCH Publishers, Inc., Deerfield Beach, FL, (1987) 365. (b) See also tables in Ref. [3a] (c) W. G. Bentrude, H.-W. Tan, K. C. Yee, J. Am. Chem. Soc., 97, 1975, 573.
23. HaHa are somewhat small: W. G. Bentrude, W. N. Setzer: in J. G. Verkade, L. Quin, (eds): Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis: Organic Compounds and Metal Complexes, VCH Publishers, Inc., Deerfield Beach, FL, (1987) 365. (b) See also tables in Ref. [3a] (c) W. G. Bentrude, H.-W. Tan, K. C. Yee, J. Am. Chem. Soc., 97, 1975, 573.
24. HaHa are somewhat small: W. G. Bentrude, W. N. Setzer: in J. G. Verkade, L. Quin, (eds): Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis: Organic Compounds and Metal Complexes, VCH Publishers, Inc., Deerfield Beach, FL, (1987) 365. (b) See also tables in Ref. [3a] (c) W. G. Bentrude, H.-W. Tan, K. C. Yee, J. Am. Chem. Soc., 97, 1975, 573.
25. 6 in chair-shared 1,3,2-dioxaphosphorinanes are in the range of 20-25 Hz; for axial protons, they are in the range of 1.5-4.5 Hz; see Ref. [13a] and L. D. Hall, R. B. Malcom, Can J. Chem., 50, 1972, 2092.
26. 6) with phosphorus: (a) W. G. Bentrude, H. Hargis, J. Am. Chem. Soc., 92, 1970, 7136; (b) W. G. Bentrude, H.-W. Tan, J. Am. Chem. Soc., 95, 1973, 4666.
27. 6) with phosphorus: (a) W. G. Bentrude, H. Hargis, J. Am. Chem. Soc., 92, 1970, 7136; (b) W. G. Bentrude, H.-W. Tan, J. Am. Chem. Soc., 95, 1973, 4666.
28. A twist conformation is more polar than an equatorial one and therefore more stabilized in polar solvents. Cf. E. L. Eliel, S. Chandrasekaran, L. E. Carpenter II, J. G. Verkade, J. Am. Chem. Soc., 108, 1986, 6651. Also, because of its more "axial-like" OAr group, its response to solvent change should be more similar to that of the axial isomers than would be expected of a conformer with purely equatorial OAr.
29. For a review of the CPMAS solid NMR technique uses and applications, see (a) C. S. Yannoni, Acc. Chem. Res., 15, 1982, 201. (b) G. E. Maciel, Science 226, 1984, 282. See also P. E. Pfeffer, J. Carbohydrate Chem., 3, 1984, 613; P. C. Healy, J. V. Hanna, J. D. Kildea, B. W. Skelton, A. H. White, Aust. J. Chem., 44, 1991, 427; W. P. Rothwell, J. S. Waugh, J. P. Yesinowski, J. Am. Chem. Soc., 102, 1980, 2637; N. Vijayashree, A. G. Samuelson, M. Nethaji, Curr. Sci., 65, 1993, 57; J. S. Waugh, Anal. Chem., 65, 1993, 725A; G. Szalontai, J. Bakos, S. Aime, R. Gobetto, Solid State Nucl. Mag. Res., 2, 1993,245; R. Challoner, C. A. McDowell, M. Yoshifuji, K. Toyota, J. A. Tossell, J. Mag. Res., Series A, 104, 1993, 258; M. Sone, H. Yoshimizu, H. Kurosu, I. Ando, J. Mol. Struct., 301, 1993, 227.
30. For a review of the CPMAS solid NMR technique uses and applications, see (a) C. S. Yannoni, Acc. Chem. Res., 15, 1982, 201. (b) G. E. Maciel, Science 226, 1984, 282. See also P. E. Pfeffer, J. Carbohydrate Chem., 3, 1984, 613; P. C. Healy, J. V. Hanna, J. D. Kildea, B. W. Skelton, A. H. White, Aust. J. Chem., 44, 1991, 427; W. P. Rothwell, J. S. Waugh, J. P. Yesinowski, J. Am. Chem. Soc., 102, 1980, 2637; N. Vijayashree, A. G. Samuelson, M. Nethaji, Curr. Sci., 65, 1993, 57; J. S. Waugh, Anal. Chem., 65, 1993, 725A; G. Szalontai, J. Bakos, S. Aime, R. Gobetto, Solid State Nucl. Mag. Res., 2, 1993,245; R. Challoner, C. A. McDowell, M. Yoshifuji, K. Toyota, J. A. Tossell, J. Mag. Res., Series A, 104, 1993, 258; M. Sone, H. Yoshimizu, H. Kurosu, I. Ando, J. Mol. Struct., 301, 1993, 227.
31. For a review of the CPMAS solid NMR technique uses and applications, see (a) C. S. Yannoni, Acc. Chem. Res., 15, 1982, 201. (b) G. E. Maciel, Science 226, 1984, 282. See also P. E. Pfeffer, J. Carbohydrate Chem., 3, 1984, 613; P. C. Healy, J. V. Hanna, J. D. Kildea, B. W. Skelton, A. H. White, Aust. J. Chem., 44, 1991, 427; W. P. Rothwell, J. S. Waugh, J. P. Yesinowski, J. Am. Chem. Soc., 102, 1980, 2637; N. Vijayashree, A. G. Samuelson, M. Nethaji, Curr. Sci., 65, 1993, 57; J. S. Waugh, Anal. Chem., 65, 1993, 725A; G. Szalontai, J. Bakos, S. Aime, R. Gobetto, Solid State Nucl. Mag. Res., 2, 1993,245; R. Challoner, C. A. McDowell, M. Yoshifuji, K. Toyota, J. A. Tossell, J. Mag. Res., Series A, 104, 1993, 258; M. Sone, H. Yoshimizu, H. Kurosu, I. Ando, J. Mol. Struct., 301, 1993, 227.
32. For a review of the CPMAS solid NMR technique uses and applications, see (a) C. S. Yannoni, Acc. Chem. Res., 15, 1982, 201. (b) G. E. Maciel, Science 226, 1984, 282. See also P. E. Pfeffer, J. Carbohydrate Chem., 3, 1984, 613; P. C. Healy, J. V. Hanna, J. D. Kildea, B. W. Skelton, A. H. White, Aust. J. Chem., 44, 1991, 427; W. P. Rothwell, J. S. Waugh, J. P. Yesinowski, J. Am. Chem. Soc., 102, 1980, 2637; N. Vijayashree, A. G. Samuelson, M. Nethaji, Curr. Sci., 65, 1993, 57; J. S. Waugh, Anal. Chem., 65, 1993, 725A; G. Szalontai, J. Bakos, S. Aime, R. Gobetto, Solid State Nucl. Mag. Res., 2, 1993,245; R. Challoner, C. A. McDowell, M. Yoshifuji, K. Toyota, J. A. Tossell, J. Mag. Res., Series A, 104, 1993, 258; M. Sone, H. Yoshimizu, H. Kurosu, I. Ando, J. Mol. Struct., 301, 1993, 227.
33. For a review of the CPMAS solid NMR technique uses and applications, see (a) C. S. Yannoni, Acc. Chem. Res., 15, 1982, 201. (b) G. E. Maciel, Science 226, 1984, 282. See also P. E. Pfeffer, J. Carbohydrate Chem., 3, 1984, 613; P. C. Healy, J. V. Hanna, J. D. Kildea, B. W. Skelton, A. H. White, Aust. J. Chem., 44, 1991, 427; W. P. Rothwell, J. S. Waugh, J. P. Yesinowski, J. Am. Chem. Soc., 102, 1980, 2637; N. Vijayashree, A. G. Samuelson, M. Nethaji, Curr. Sci., 65, 1993, 57; J. S. Waugh, Anal. Chem., 65, 1993, 725A; G. Szalontai, J. Bakos, S. Aime, R. Gobetto, Solid State Nucl. Mag. Res., 2, 1993,245; R. Challoner, C. A. McDowell, M. Yoshifuji, K. Toyota, J. A. Tossell, J. Mag. Res., Series A, 104, 1993, 258; M. Sone, H. Yoshimizu, H. Kurosu, I. Ando, J. Mol. Struct., 301, 1993, 227.
34. For a review of the CPMAS solid NMR technique uses and applications, see (a) C. S. Yannoni, Acc. Chem. Res., 15, 1982, 201. (b) G. E. Maciel, Science 226, 1984, 282. See also P. E. Pfeffer, J. Carbohydrate Chem., 3, 1984, 613; P. C. Healy, J. V. Hanna, J. D. Kildea, B. W. Skelton, A. H. White, Aust. J. Chem., 44, 1991, 427; W. P. Rothwell, J. S. Waugh, J. P. Yesinowski, J. Am. Chem. Soc., 102, 1980, 2637; N. Vijayashree, A. G. Samuelson, M. Nethaji, Curr. Sci., 65, 1993, 57; J. S. Waugh, Anal. Chem., 65, 1993, 725A; G. Szalontai, J. Bakos, S. Aime, R. Gobetto, Solid State Nucl. Mag. Res., 2, 1993,245; R. Challoner, C. A. McDowell, M. Yoshifuji, K. Toyota, J. A. Tossell, J. Mag. Res., Series A, 104, 1993, 258; M. Sone, H. Yoshimizu, H. Kurosu, I. Ando, J. Mol. Struct., 301, 1993, 227.
35. For a review of the CPMAS solid NMR technique uses and applications, see (a) C. S. Yannoni, Acc. Chem. Res., 15, 1982, 201. (b) G. E. Maciel, Science 226, 1984, 282. See also P. E. Pfeffer, J. Carbohydrate Chem., 3, 1984, 613; P. C. Healy, J. V. Hanna, J. D. Kildea, B. W. Skelton, A. H. White, Aust. J. Chem., 44, 1991, 427; W. P. Rothwell, J. S. Waugh, J. P. Yesinowski, J. Am. Chem. Soc., 102, 1980, 2637; N. Vijayashree, A. G. Samuelson, M. Nethaji, Curr. Sci., 65, 1993, 57; J. S. Waugh, Anal. Chem., 65, 1993, 725A; G. Szalontai, J. Bakos, S. Aime, R. Gobetto, Solid State Nucl. Mag. Res., 2, 1993,245; R. Challoner, C. A. McDowell, M. Yoshifuji, K. Toyota, J. A. Tossell, J. Mag. Res., Series A, 104, 1993, 258; M. Sone, H. Yoshimizu, H. Kurosu, I. Ando, J. Mol. Struct., 301, 1993, 227.
36. For a review of the CPMAS solid NMR technique uses and applications, see (a) C. S. Yannoni, Acc. Chem. Res., 15, 1982, 201. (b) G. E. Maciel, Science 226, 1984, 282. See also P. E. Pfeffer, J. Carbohydrate Chem., 3, 1984, 613; P. C. Healy, J. V. Hanna, J. D. Kildea, B. W. Skelton, A. H. White, Aust. J. Chem., 44, 1991, 427; W. P. Rothwell, J. S. Waugh, J. P. Yesinowski, J. Am. Chem. Soc., 102, 1980, 2637; N. Vijayashree, A. G. Samuelson, M. Nethaji, Curr. Sci., 65, 1993, 57; J. S. Waugh, Anal. Chem., 65, 1993, 725A; G. Szalontai, J. Bakos, S. Aime, R. Gobetto, Solid State Nucl. Mag. Res., 2, 1993,245; R. Challoner, C. A. McDowell, M. Yoshifuji, K. Toyota, J. A. Tossell, J. Mag. Res., Series A, 104, 1993, 258; M. Sone, H. Yoshimizu, H. Kurosu, I. Ando, J. Mol. Struct., 301, 1993, 227.
37. For a review of the CPMAS solid NMR technique uses and applications, see (a) C. S. Yannoni, Acc. Chem. Res., 15, 1982, 201. (b) G. E. Maciel, Science 226, 1984, 282. See also P. E. Pfeffer, J. Carbohydrate Chem., 3, 1984, 613; P. C. Healy, J. V. Hanna, J. D. Kildea, B. W. Skelton, A. H. White, Aust. J. Chem., 44, 1991, 427; W. P. Rothwell, J. S. Waugh, J. P. Yesinowski, J. Am. Chem. Soc., 102, 1980, 2637; N. Vijayashree, A. G. Samuelson, M. Nethaji, Curr. Sci., 65, 1993, 57; J. S. Waugh, Anal. Chem., 65, 1993, 725A; G. Szalontai, J. Bakos, S. Aime, R. Gobetto, Solid State Nucl. Mag. Res., 2, 1993,245; R. Challoner, C. A. McDowell, M. Yoshifuji, K. Toyota, J. A. Tossell, J. Mag. Res., Series A, 104, 1993, 258; M. Sone, H. Yoshimizu, H. Kurosu, I. Ando, J. Mol. Struct., 301, 1993, 227.
38. For a review of the CPMAS solid NMR technique uses and applications, see (a) C. S. Yannoni, Acc. Chem. Res., 15, 1982, 201. (b) G. E. Maciel, Science 226, 1984, 282. See also P. E. Pfeffer, J. Carbohydrate Chem., 3, 1984, 613; P. C. Healy, J. V. Hanna, J. D. Kildea, B. W. Skelton, A. H. White, Aust. J. Chem., 44, 1991, 427; W. P. Rothwell, J. S. Waugh, J. P. Yesinowski, J. Am. Chem. Soc., 102, 1980, 2637; N. Vijayashree, A. G. Samuelson, M. Nethaji, Curr. Sci., 65, 1993, 57; J. S. Waugh, Anal. Chem., 65, 1993, 725A; G. Szalontai, J. Bakos, S. Aime, R. Gobetto, Solid State Nucl. Mag. Res., 2, 1993,245; R. Challoner, C. A. McDowell, M. Yoshifuji, K. Toyota, J. A. Tossell, J. Mag. Res., Series A, 104, 1993, 258; M. Sone, H. Yoshimizu, H. Kurosu, I. Ando, J. Mol. Struct., 301, 1993, 227.
39. 31P NMR spectrum of a sample spinning at the magic angle at rotation speeds that are below the powder line width was flanked by spinning side bands. See, for example, (a) T. Chivers, M. Edwards, C. A. Fyfe, L. H. Randall, Mag. Res. Chem., 30, 1992, 1220; (b) J. D. Wang, A. Clearfield, Mat. Chem. Phys., 35, 1993, 208; R. Contant, C. Rocchiccioli-Deltcheff, M. Fournier, R. Thouvenot, Colloids. Surf. A: Physicochem, Eng. Asp., 72, 1993, 301.
40. 31P NMR spectrum of a sample spinning at the magic angle at rotation speeds that are below the powder line width was flanked by spinning side bands. See, for example, (a) T. Chivers, M. Edwards, C. A. Fyfe, L. H. Randall, Mag. Res. Chem., 30, 1992, 1220; (b) J. D. Wang, A. Clearfield, Mat. Chem. Phys., 35, 1993, 208; R. Contant, C. Rocchiccioli-Deltcheff, M. Fournier, R. Thouvenot, Colloids. Surf. A: Physicochem, Eng. Asp., 72, 1993, 301.
41. 31P NMR spectrum of a sample spinning at the magic angle at rotation speeds that are below the powder line width was flanked by spinning side bands. See, for example, (a) T. Chivers, M. Edwards, C. A. Fyfe, L. H. Randall, Mag. Res. Chem., 30, 1992, 1220; (b) J. D. Wang, A. Clearfield, Mat. Chem. Phys., 35, 1993, 208; (c) R. Contant, C. Rocchiccioli-Deltcheff, M. Fournier, R. Thouvenot, Colloids. Surf. A: Physicochem, Eng. Asp., 72, 1993, 301.
42. The spectrum was complicated by the presence of extra signals (repetitive pattern) in the aromatic region due to the large chemical shift anisotropy typical for phenyl rings. See Ref. [21].
43. (a) Colin A. Fyfe: Solid State NMR for Chemist, C. F. C. Press, Guelph, Ont., Canada (1983):
44. (b) P. Knopik, L. Luczak, M. J. Potrzebowski, J. Michalski, J. Blaszczyk, M. W. Wieczorek, J. Chem. Soc. Dalton Trans., p. 2749 (1993);
45. (c) M. J. Potrzebowski, J. Chem. Soc. Perkin Trans., 2, 1993, 63.
46. Using the NRCVAX system: E. J. Gabe, Y. LePage, J. P. Charland, F. L. Lee, P. S. White, J. Appl. Cryst., 22, 1989, 384.
47. Concerning the ORTEP structures shown, cf. C. K. Johnson: ORTEP - A Fortran Thermal Ellipsoid Plot, Technical Report ORNL-5138, Oak Ridge Laboratories, Oak Ridge, TN (1976).
48. It should be noted that the numbering system in the structures simultaneously submitted to the Cambridge Crystallographic Data Base is different from that used here.
49. (a) D. W. J. Cruickshank, J. Chem. Soc., 1961, 5486;
50. (b) H. J. Geise, Rec. Trav. Chim. Pays-Bas, 86, 1967, 362.
51. For a similar analysis in analogs, see R. W. Warrent, C. N. Caughlan, J. H. Hargis, K. C. Yee, W. G. Bentrude, J. Org. Chem., 43, 1978, 4266.
52. 2, on phosphorus is axial: B. Lilo, M. Moreau, D. Bouchu, Tetrahedron Lett., 31, 1990, 887; see also L. E. Carpenter II, D. Powell, R. A. Jacobson, J. G. Verkade, Phosphorus and Sulfur, 12, 1982, 287.
53. 2, on phosphorus is axial: B. Lilo, M. Moreau, D. Bouchu, Tetrahedron Lett., 31, 1990, 887; see also L. E. Carpenter II, D. Powell, R. A. Jacobson, J. G. Verkade, Phosphorus and Sulfur, 12, 1982, 287.
54. The conformations of oxazaphosphorinanes can be attributed to the operation of exo and endo anomeric effects: W. G. Bentrude, W. N. Setzer, M. G. Newton, E. J. Meehan, Jr., E. Ramli, M. Khan, S. Ealick, Phosphorus, Sulfur and Silicon, 57, 1991, 25; W. G. Bentrude, W. N. Setzer, A. A. Kergaye, V. Ethridge, M. R. Saadein, Atta M. Arif, Phosphorus, Sulfur and Silicon, 57, 1991, 37.
55. The conformations of oxazaphosphorinanes can be attributed to the operation of exo and endo anomeric effects: W. G. Bentrude, W. N. Setzer, M. G. Newton, E. J. Meehan, Jr., E. Ramli, M. Khan, S. Ealick, Phosphorus, Sulfur and Silicon, 57, 1991, 25; W. G. Bentrude, W. N. Setzer, A. A. Kergaye, V. Ethridge, M. R. Saadein, Atta M. Arif, Phosphorus, Sulfur and Silicon, 57, 1991, 37.
56. D. F. Ewing, Org. Mag. Res., 12, 1979, 499.