Stereoselective benzannulations and cyclohexadienone annulations of Fischer carbene complexes in the synthesis of decala-2,4-dien-1-ones and in the synthesis of tetralin chromium tricarbonyl complexes

Article abstract of DOI:10.1055/s-1996-4292

The first general study is reported on the stereoselectivity of the benzannulation reaction involving diastereoselection at the planar center of chirality of the newly formed arene ring complexed to chromium that is induced from a chiral carbon center on the carbene complex. The stereochemistry of a number of 5- and 8-substituted tetralin chromium tricarbonyl complexes, which are produced from the benzannulations of cyclohexenyl carbene complexes with chiral centers at the 3- and 6-positions, is determined. These results are compared with the stereochemistry of the formation of 5,9- and 8,9-disubstituted decala-2,4-dien-1-ones produced from the reactions of the same carbene complexes bearing an additional substituent in the 2-position of the cyclohexenyl ring. The benzannulation reaction is most selective with 3-substituted cyclohexenyl carbene complexes giving predominately the anti-isomer of the 8-substituted tetralin chromium tricarbonyl complexes. In contrast, the cyclohexadienone annulation is most selective with 6-substituted cyclohexenyl carbene complexes giving predominately the trans-isomer of the 5,9-disubstituted decala-2,4-dien-1-ones. A mechanistic accounting of the stereochemical results is proposed which is predicated on three assumptions: 1) that the η¹,η³-vinyl carbene complexed intermediate is in equilibrium, 2) vinyl ketene complex formation is irreversible and occurs with a carbon monoxide migration that is in concert with coordination of the double bond of the cyclohexene ring, and 3) the electrocyclic ring closure of the vinyl ketene complex is stereospecific.