ORGANOIRON COMPLEXES IN ORGANIC-SYNTHESIS .3. APPROACH TO THE SYNTHESIS OF SPIROCYCLIC COMPOUNDS FROM TRICARBONYLDIENE-IRON COMPLEX INTERMEDIATES

Synthesis of methyl 8-methoxy-2-oxospiro[4.5]deca-6,8-diene-3-carboxylate (14) in eight steps from p-methoxycinnamic acid is described. The method involves cyclisation of the 1,1-disubstituted-cyclohexa-2,4-diene (2d) which is readily obtained from tricarbonyl[η-1-5-1-(3′-methoxycarbonylpropyl)- 4-methoxycyclohexa-2,4-dienylium]iron hexafluorophosphate (3b). A similar series of reactions starting from 4-(p-methoxyphenyl) butyric acid leads ultimately to methyl 3-methoxy-8-oxospiro[5.5]undeca-1,3-diene-9-carboxylate (16). In the course of investigating model systems the trichodermin intermediate (1c) has also been synthesised.