摘要:
Enantioselective protonation of the s-BuLi derived lithium enolate of (S)-phenyl 1,4-dioxa-8-thia-spiro[4.5]decane-6-carbothioate 14 with N-isopropylephedrine 15 gives 14 as a 10:1 mixture of enantiomers. Recrystallization of nonracemic 14 gives a highly enantioenriched material (>90% ee), which can be converted into 1,4-dioxa-8-thia-spiro[4.5]decane-6-carboxaldehyde 2 without racemization. Diastereoselective aldol reactions of tetrahydro-4H-thiopyran-4-one with nonracemic 2 proceed with negligible racemization to give adducts that are useful building blocks for polypropionate synthesis. (C) 2004 Elsevier Ltd. All rights reserved.