Iterative, Stereoselective Homologation of Chiral Polyalkoxy Aldehydes Employing 2-(Trimethylsilyl)thiazole as a Formyl Anion Equivalent. The Thiazole Route to Higher Carbohydrates

A new approach to long-chain sugars is demonstrated by the stereoselective conversion of D-glyceraldehyde acetonide (2a), L-threose acetonide (2b), and dialdogalactopyranose diacetonide (2h) into higher homologues up to C9, C7, and C10terms, respectively, and with an all-anti configuration of vicinal hydroxy groups in the constructed chain. The methodology consists of the iterative repetition of a linear one-carbon chain extension that involves two very efficient (chemically and stereochemically) key operations: (A) the anti diastereoselective addition of 2-(trimethylsilyl)thiazole (la) to the chiral alkoxy aldehyde; the unmasking of the formyl group from the thiazole ring in the resulting adduct. The conversion of thiazole D-ribose 9a into protected 2-deoxy-and 2,5-dideoxy-D-ribose (28 and 30) demonstrates the synthetic potential of thiazole masked sugars. © 1989, American Chemical Society. All rights reserved.