Enamine chemistry. Part 37. Reaction of methyl vinyl ketone with Δ1,8a-2-octalone dienamines. Synthesis of octahydro-1H-benzo[d]naphthalene-2,10(3H,11H)-diones and 9-acetylperhydro-2,4a-ethanonaphthalen-3-ones

Abstract

Reaction of the pyrrolidine dienamines of Δ^1,8a-2-octalones with methyl vinyl ketone is complex. In methanol as solvent reaction occurs primarily with the linear dienamine isomer and results in annulation of the 8,8a-positions and, to a lesser extent, the 1,2-positions to give the corresponding octahydro-1H-benzo[d]naphthalene-2,10(3H,11H)-dione and 4,5,6,7,8,8a,9,10-octahydrophenanthren-2(3H)-one respectively. In toluene the dienamines react mainly in their cross-conjugated form. Diels–Alder addition of methyl vinyl ketone occurs across the 3,8a-positions to give the corresponding 9-acetylperhydro-2,4a-ethanonaphthalen-3-one, and annulation of the 2,3-positions gives the 4,4a,5,5a,6,7,8,9-octahydroanthracen-2(3H)-one. The mechanism of formation and spectral properties of the various products are discussed. Long-range shielding or deshielding effects arising from the proximity of stereochemically rigid C–C and C–H bonds are noted, the magnitude of which is sufficient to nullify or overcome the deshielding influence of neighbouring carbonyl groups.