RADICAL-TYPE CYCLIZATION OF DIENES .5. - SUBSTRATE-CONTROLLED ASYMMETRIC-SYNTHESIS OF (-)-HIRSUTENE AND (-)-3-HYDROXYHIRSUTENE FROM (R)-(-)-CARVONE

l-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-2-one (6) and 3-methyl-cy clopent-2-enyl]-2,2-dimethylpropan-1-ol (11) are key compounds in the synthesis reported in this paper. Enantiomerically pure 6 was obtained in five straightforward steps from the inexpensive precursor (R)-(-)- carvone (1). Compound 11 was prepared from 6 via an S(N)2' reaction, b y analogy with the synthesis reported by Curran et al. The linear triq uinanes 13 and 15 were obtained in gram quantities in two additional s teps. The utilisation of (S)-(+)-carvone (ent-1) allows access to the other enantiomeric forms. X-ray analysis of 15a confirmed the structur e of 15 and, by correlation, that of 13.