Enantiopure building blocks for the synthesis of 3-methyl-2-alkanols. Diastereoselective methylmetal addition to a chiral 2-methylaldehyde followed by lipase catalysed esterification
2004 (English)In: Tetrahedron: asymmetry, ISSN 0957-4166, E-ISSN 1362-511X, Vol. 15, 2907-2915 p.Article in journal (Refereed) Published
The racemic synthetic building block (2R*,3R*)-3-methyl-4-(phenylsulfanyl)butan-2-ol (2R*,3R*)-2 was obtained in a high diastereomeric ratio [95:5, (2R*,3R*)/(2R*,3S*)-ratio] by Lewis acid catalysed dimethylzinc addition to racemic 2-methyl-3-(phenylsulfanyl)propanal (rac-1). Two consecutive acylations with vinyl acetate catalysed by Chirazyme L-2 (immobilised Candida antarctica lipase 13, CAL-B) led to preferential esterification of three of the four stereoisomers leaving (2S,3S)-3-methyl-4-(phenylsulfanyl)butan-2-ol (2S,3S)-2 of 98:2 dr and 98% ee. The stereoisomerically impure acetate of (2R,3R)-3-methyl-4-(phenyisulfanyl)butan-2-ol (2R,3R)-2, obtained in the first CAL-B-catalysed acylation step, was hydrolysed and reesterified using CAL-A (immobilised Novozyme SP 525) as the catalyst, which left (2R,3R)-3-methyl-4-(phenylsulfanyl)butan-2-ol (2R,3R)-2 of 98:2 dr and 99% ee as the remaining substrate. The individual enantiomers of 2-methyl-3-(phenylsulfanyl)propanal 1 were prepared from readily available (S)- and (R)-3-hydroxy-2-methylpropanoic acid methyl ester and reacted with dimethylzinc to give both enantiomers of (2R*,3R*)-3-methyl-4-(phenylsulfanyl)butan-2-ol (2R, 3R)- or (2S,3S)-2 of both high dr and ee. These products were purified by lipase catalysed acylation to give the enantiomerically and diastereomerically highly pure enantiomers (>99.5:0.5 dr, >99.9% ee). Pure (2S,3S)-3-methyl-4-(phenylsulfanyl)butan-2-ol (2S,3S)-2 was transformed into a potential pheromone precursor isolated from some pine sawflies of the genus Gilpinia, (2S,3R)-3-methylpentadecan-2-ol in 54% yield over eight steps.
Place, publisher, year, edition, pages
2004. Vol. 15, 2907-2915 p.
hypophosphite combination system, enantioselective total synthesis, candida-antarctica lipase, sex-pheromone, secondary alcohols, raney-nickel, reductive desulfurization, macrodiprion-nemoralis, microdiprion-pallipes, neodiprion-sertifer
IdentifiersURN: urn:nbn:se:kth:diva-6646DOI: 10.1016/j.tetasy.2004.07.049ISI: 000224333100032OAI: oai:DiVA.org:kth-6646DiVA: diva2:11411
QC 201010202005-09-212005-09-212010-10-26Bibliographically approved