1,5-Remote stereocontrol using allylgermanes

Tetrahedron Letters

Volumn 48, Issue 3, 2007, Pages 337-340

  Castreno, Pilar ^a   Thomas, Eric J ^a   Weston, Anna P ^a  

^a UNIVERSITY OF MANCHESTER   (United Kingdom)

Author keywords

Allylmetal; Diastereoselectivity; Organogermanium; Remote stereocontrol

Indexed keywords

ALDEHYDE DERIVATIVE; ALLYL COMPOUND; ALLYLGERMANE DERIVATIVE; ALLYLTIN TRICHLORIDE; GERMANIUM DERIVATIVE; PENT 2 ENYLGERMANE DERIVATIVE; TIN CHLORIDE;

ARTICLE; CHEMICAL REACTION; METALLATION; REMOTE STEREOCHEMICAL CONTROL; STEREOCHEMISTRY; STEREOSPECIFICITY;

EID: 33845385656     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/j.tetlet.2006.11.065     Document Type: Article

References (21)

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5. Martin N., and Thomas E.J. Tetrahedron Lett. 42 (2001) 8373
6. Germay O., Kumar N., and Thomas E.J. Tetrahedron Lett. 42 (2001) 4969
7. Brain C.T., and Thomas E.J. Tetrahedron Lett. 38 (1997) 2387
8. Beddoes R., Hobson L.A., and Thomas E.J. J. Chem. Soc., Chem. Commun. (1997) 1929
9. Akiyama T., and Suzuki M. Chem. Commun. (1997) 2357
10. Spivey A.C., and Diaper D.H. In: Molony M.G. (Ed). Science of Synthesis: Houben Weyl Methods of Molecular Transformations Vol. 5 (2002), Thieme, Stuttgart 181
11. Hagen G., and Mayr H. J. Am. Chem. Soc. 113 (1991) 4954
12. The (2E)- and (2Z)-acetates 9 were prepared from the corresponding alcohols (see Ref. 2). Details will be included in a full paper.
13. Yamaguchi J., Tamada Y., and Takeda T. Bull. Chem. Soc., Jpn. 66 (1993) 607
14. 1H NMR by the integration of benzylic and methyl protons.
15. If the aldehyde was added to the reaction mixture before transmetallation was complete, complex mixtures of products were obtained which appeared to include branched product i, as a mixture of stereoisomers, possibly formed by the reaction of allylgermane with the Lewis acid co-ordinated aldehyde. Transmetallation times of less than 15 min were possible with increased concentrations of reactants (cf. Table 2, entry 2), but allowing 15 min for this process proved reliable, convenient and maintained useful levels of stereoselectivity.{A figure is presented}
16. 1H NMR spectra by integration of the benzylic and methyl protons, which were distinct for 1,5-anti- and -syn-diastereoisomers. These ratios were also confirmed for products 3b/11b and 3c/11c, by comparison of their 4-nitrobenzoates prepared by a direct esterification, and by esterification with inversion of configuration using a Mitsunobu reaction. Comparison of 4-nitrobenzoates also provided the product ratios for products 3f/11f, 3g/11g and 3i/11i.
17. These transmetallations are believed to take place via antarafacial SE′ processes with the trichlorotin group delivered by the oxygen of the benzyloxy substituent, the diastereofacial selectivity being controlled by the preference of the 4-methyl substituent to adopt the less hindered 'outside' rather than the more hindered 'inside' position (see Ref. 1). These steric interactions may be larger for (2Z)-pent-2-enyl isomers so leading to the slightly better overall stereoselectivity observed for (2Z)-pent-2-enylgermanes.{A figure is presented}
18. The overall stereoselectivities observed using the 55:45 mixture of the (2E)- and (2Z)-pentenyl(triphenyl)germanes appeared to be slightly higher than would have been predicted from the results using the separate (2E)- and (2Z)-isomers (cf. Table 2, entries 1-5). The reason for this has not been elucidated.
19. Acetate 12 was prepared from the corresponding alcohol (see Ref. 19).
20. MacNeill A.H., and Thomas E.J. Synthesis (1994) 322
21. +-17, 90%).