Hydroxy-2-penten&lide (5) was synthesized in three stcps starting from mnannitol bidacetonide) (l), via Dglyceraldchydc acetonide (2) by Z-selective Wittig reaction, acid-catalyzed lactonization and crystallization with a total yield of 40%.
(S)-S-Hydroxy-2-penten-4-0lide (S), the aglycone of ranunculine 'I, as well as derivatives thereof, increasingly serve as building blocks in syntheses of optically active products. The various routes either rely on the Sharpless asymmetric epoxidation [of (Z)-4-bcnzyloxy-2-butcnol] 3', or use the "ehiral pool" approach starting from L-glutamic acid4), 1,-ribonolactone 5'6), and, very recently, from n-mannitol bis(acetonide) (1) via 2,3-O-isopropylidcne-~-glyceraldehyde (D-IGA) (2)738). The latter papers describe routes via saturated lactones, obtained after C2-elongation of 2 by means of an E-selective Wittig reaction') or acetate enolate addition 'I, with over-all yields of 59% after 5 steps from l", and of 36%, after 4 steps, from 28', respectively. This prompts us to detail the simple ca. 40%/3 step preparation of 5 from 1 announced earlier9), which allows to obtain crystalline 5 in superior optical purity on a multi-gram scale.