Organoiron complexes in organic synthesis. Part 3. An approach to the synthesis of spirocyclic compounds from tricarbonyldieneiron complex intermediates

Abstract

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.