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The palladium-catalyzed asymmetric 4+3 cyclization of trimethylenemethane donors with benzofuran-derived azadienes furnishes chiral benzofuro3,2-bazepine frameworks in high yields (up to 98 %) with exclusive regioselectivities and excellent stereoselectivities (up to >20:1 d.r., >99 % ee). This catalytic asymmetric 4+3 cyclization of Pd-trimethylenemethane can enrich the arsenal of Pd-TMM reactions in organic synthesis. In addition, this strategy provides an alternative approach to chiral azepines by a transition-metal-catalyzed asymmetric 4+3 cyclization.
Liu et al. (Fri,) studied this question.