10.1016/S0040-4039(00)01093-5
The study focuses on the synthesis of (+)-alloyohimbane, a yohimbine alkaloid, using the intramolecular Diels-Alder reaction of N-acylvinyl imidates as a key methodology. This approach provides a rapid entry into cis-fused hexahydroisoquinolones, which are essential for constructing the DE rings of yohimbine alkaloids. The chemicals used in the study include sorbic acid, LDA (lithium diisopropylamide), acid chloride, 2-ethoxy-1-aza-1,3-butadiene, benzene, NaBH3CNBH3 (sodium cyanoborohydride), TFA (trifluoroacetic acid), and various other reagents for the synthesis and transformation of intermediates. These chemicals serve to deconjugate sorbic acid, form the Diels-Alder precursor, effect the cycloaddition to form the cycloaddduct, and subsequently reduce and modify the product to afford the target lactam and ultimately (+)-alloyohimbane. The study also developed a radical-based strategy for synthesizing indoline electrophiles from o-bromoaniline derivatives, which are crucial for the synthesis of substituted indolines and the completion of the alkaloid structure.