ASYMMETRIC-SYNTHESIS OF ENT-COREY LACTONE ALCOHOL AND ITS 12-(ALL-CIS)- AND 11-EPIMERS VIA FREE-RADICAL 5-EXO-TRIG-C,C CYCLIZATION

Asymmetric eight-step syntheses are reported for the ent-Corey lactone alcohol derivatives 3a-d and their epimers 4a-d and 14a, b from (R)-2 ,3-isopropylidene glyceraldehyde (5) as the starting material. The key step of the synthesis is the free radical cyclization of the butenoli de thiocarbonates 11, 12 and 13. This reaction produces 3 and 4 in rat ios between 57:43 and 30:70 from 11 and 12, whereas 14a and 14b are ge nerated from 13 in a ratio of 19:81. From 3d the prostanoid enone 18 i s prepared via the configurationally stable aldehyde 17.