Applications of 5-Endo-trigonal Cyclization: Construction of Compounds Relevant to the Synthesis of Prostaglandins and Methyl epi-Jasmonate.

Silane 15, easily constructed by simple methods, undergoes a cascade of radical reactions when treated with a stannane to afford the bicyclic 1,2-oxasiloles 16, with the major isomer having the ester group anti to the O-Si unit. This isomer was elaborated via 19 into 6, a deoxy derivative of the Corey lactone. In a related sequence, ketone 24 was converted into silane 35; this, too, underwent the radical cascade to afford the highly substituted 1,2-oxasiloles 36. Again the major isomer had the ester and O-Si units in an anti relationship. Elaboration of 36 (major isomer) gave the Corey lactone derivative 7. A key intermediate (32) in this second sequence was also prepared in optically pure form by starting with 2-deoxy-D-ribose. Compound 19 was converted into 8, a sequence that constitutes a formal synthesis of methyl (+/-)-epi-jasmonate. Two examples were found of selective silylation of a propargylic secondary hydroxyl in the presence of an ordinary secondary hydroxyl.