STEREOCHEMISTRY, CONFORMATIONAL-ANALYSIS, AND TRANS-ANNULAR CYCLIZATIONS OF NINE-MEMBERED RING AZAOLEFINS

A transannular route to the indolizidine ring system (3) via an intramolecular cyclization of the appropriate azaolefins is described. Treatment of 1H-2, 3, 4, 7, 8, 9-hexahydroazonine (7b) with either bromine or mercuric chloride affords, after reduction, the indolizidine alkaloid, δ-coniceine (15). The lactam analogue 1, 3, 4, 7, 8, 9-hexahydro-2H-azonin-2-one (7a) also undergoes regiospecific ring closure when treated with a suitable electrophile (mercuric acetate) to yield the indolizinone skeleton 21. Similar alkyl-substituted compounds were prepared and the products cyciized stereoseiectively. The synthetic consequence of this reaction as well as the mechanistic implications are discussed. © 1979, American Chemical Society. All rights reserved.