STEREOCHEMISTRY ASSOCIATED WITH THE ADDITION OF 2-(TRIMETHYLSILYL)THIAZOLE TO DIFFERENTIALLY PROTECTED ALPHA-AMINO ALDEHYDES - APPLICATIONS TOWARD THE SYNTHESIS OF AMINO-SUGARS AND SPHINGOSINES

The stereochemistry and synthetic utility of the addition of 2-(trimethylsilyl)thiazole (2-TST, 1) to various N-protected a-amino aldehydes is described. The reactions of 1 with N-Boc-L-serinal acetonide (2) and N-Boc-L-threoninal acetonide (3) are essentially anti diastereoselective (ds = 85-90%) in agreement with the Felkin-Anh model for asymmetric induction, whereas the reactions with O-benzyl-NH-Boc-L-serinal (4) and NH-Boc-L-phenylalaninal (5) are syn diastereoselective (ds = 80%). The reversal of diastereoselectivity is interpreted on the basis of a proton-bridged cyclic Cram model for asymmetric induction. The anti adduct derived from the N-Boc-L-serinal acetonide (2) was subjected to thiazole-to-formyl unmasking to give a one-carbon higher homologue (i.e., the 0, N-protected β-amino-α-hydroxy aldehyde 6a). This material serves as a precursor to ribo-and arabino-4-amino-4-deoxypentoses via a further one-carbon-chain elongation with 2-TST and to a C20 sphingosine via Wittig olefination. The above ribo-amino sugar was transformed via sequential Wittig olefination and reduction into a C18 phytosphingosine. © 1990, American Chemical Society. All rights reserved.