Approaches to the synthesis of cytochalasans. Part 8 . Further transformations and optical resolution of the tetrahydroisoindolinone subunit

The bicycle aldehyde 7 was prepared from the hydroxy ester 3 for the attachment of teh macrocyclic moiety of the cytochalasans. To protect the C(6),C(7)‐double bond the intermediates 8 , 9 and 13 were transformed into the epoxides 10 , 11 and 14 , respectively. Treatment of 10 and 11 with Al(i‐PrO) 3 gave the allylic alcohol 12 . Protection of the olefinic double bond was also effected by hydroxylation with OsO 4 . The triol 17 obtained from 3 , after acetalization of 18 , was oxidized to the aldehyde 20 . Attachment of the ylide of the phosphonium salt 1 to 20 gave 24 , an intermediate of proxiphomin ( 2 ). Removal of the C(6), C(7)‐diol group was achieved via the thiocarbonate 23 .