Stereochemistry Associated with the Addition of 2-(Trimethylsilyl)thiazole to Differentially Protected α-Amino Aldehydes. Applications toward the Synthesis of Amino Sugars ans Sphingosines

Article abstract of DOI:10.1021/jo00292a013

The stereochemistry and synthetic utility of the addition of 2-(trimethylsilyl)thiazole (2-TST, 1) to various N-protected α-amino aldehydes is described.The reactions of 1 with N-Boc-L-serinal acetonide (2) and N-Boc-L-threoninal acetonide (3) are essential anti diastereoselective (ds = 85-90percent) 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 = 80percent).The reversal of diastereoselectivity is interpreted on the basis of a proton-bridged cyclic Cram model for asymmetric induction.Te anti-adduct derived the N-Boc-L-serinal acetonide (2) was subjected to thiazol-to-formyl unmasking to give a one-carbon higher homologue (i. e., the O,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.