A highly dl-stereoselective pinacolization of aromatic aldehydes mediated by titanium trichloride in dichloromethane

Tetrahedron Letters

Volumn 37, Issue 17, 1996, Pages 3035-3038

  Clerici, Angelo ^a   Clerici, Laura ^a   Porta, Ombretta ^a  

^a POLITECNICO DI MILANO   (Italy)

Author keywords

[No Author keywords available]

Indexed keywords

ALKANEDIOL DERIVATIVE;

ARTICLE; DRUG SYNTHESIS; REACTION ANALYSIS; STEREOCHEMISTRY;

EID: 0029879081     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/0040-4039(96)00462-5     Document Type: Article

References (29)

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9. b) Szymaniak, J.; Besançon, J.; Moise, C. ibid. 1994, 50, 2841;
10. b) Anionic zirconaoxirane leads to a 19:1 mixture of dl/meso hydrobenzoin: Askhan, F. R.; Caroll, K. M. J. Org. Chem. 1993, 58, 7328.
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19. In aqueous solution, the reducing power of Ti(III) redox-system is strongly pH dependent and hydrodimerization of benzaldehyde occurs only in strong basic media but, owing to the low coordination power of Ti(IV) under these conditions, diastereoselectivity is very poor (dl/meso ratio: 1.3): a) Clerici, A.; Porta, O. Tetrahedron Lett. 1982, 23, 3517;
20. b) Clerici, A; Porta, O. J.Org. Chem. 1985, 50, 76.
21. Available from Aldrich.
22. The change of colour observed during the reaction depends upon the nature of the aryl substituent.
23. 1H NMR prior to any further manipulation.
24. On standing, the dl-diol condenses with the unreacted aldehyde affording the corresponding dl-2,4,5-triaryl-1,3-dioxolane: see also ref. 6.
25. Ti(III) and TI(IV) furnish well defined 1:1 and 1:2 oxygen-donor complexes with benzaldehyde, respectively. a) Coutts, R. S. P.; Wailes, P. C.; Martin, R. L. J. Organomet: Chem. 1973, 50, 145;
26. b) Pellissier, H.; Toupet, L.; Santelli, M. J. Org. Chem. 1994, 59, 1709.
27. Duthaler, R. O.; Haufer, A. Chem. Rev. 1992, p 813 and references cited herein.
28. The reduction of benzaldehyde in the presence of (+)dimethyltartrate (entry 1d) is slightly enantioselective (4% opt. yield of (-)hydrobenzoin).
29. 1H NMR spectra of the crude reaction mixture with that of an authentic mixture of dl and mesa isomers. The dl/meso ratio of entries 2-6 is less accurate since we tentatively assigned the very small signal at ca 0.1-0.2 ppm lower field to the meso isomer (see ref. 8).