Efficient and versatile synthesis of (2S,3R)-sphingosine and its 2-azido-3-O-benzylsphingosine analogue

The title compounds (1, 2) were synthesized from (2R,3S)-2-O-benzyl-3,4-O-(3′-pentylidene)-2,3,4-trihydroxybutanal (5). Installation of the E-double bond and aliphatic chain into the sphingosine base was effected by a sequence of Horner-Wadsworth-Emmons olefination of 5, conversion to allylic acetate 8, and copper-mediated Grignard coupling. The method is versatile, allowing a broad variety of aliphatic chains to be introduced in the organocuprate coupling step.