Rhodium(III)-Catalyzed Asymmetric Reductive Cyclization of Cyclohexadienone-Containing 1,6-Dienes via an Anti-Michael/Michael Cascade Process

Ring
strain plays an important role in metal-catalyzed cyclization
of 1,6-dienes. Herein, we report a rhodium­(III)-catalyzed asymmetric
reductive cyclization of cyclohexadienone-tethered α,β-unsaturated
compounds (1,6-dienes), including α,β-unsaturated ketones,
esters, amides, sulfone, and phosphonate. The reactions undergo an
unusual anti-Michael/Michael addition process, affording cis-bicyclic frameworks with good to high yields and good diastereo-
and enantioselectivities. Furthermore, several transformations of
the products and a one-pot preparation of bridged polycyclic structure
are also presented. Finally, DFT calculations show that the enantioselectivity
is determined by the initial olefin insertion step and that the ring
strain controls the overall regioselectivity and favors the formation
of 5,6-bicyclic products.

环张力（Ring strain）在金属催化的1,6-二烯环化反应中发挥着重要作用。本文报道了一种铑(III)催化的不对称还原环化反应，以连有环己二酮结构的α,β-不饱和化合物（1,6-二烯类）为底物，该类底物包括α,β-不饱和酮、酯、酰胺、砜以及膦酸酯。该反应经历了反常的反-Michael/Michael加成历程，以良好至较高的收率以及良好的非对映选择性和对映选择性得到顺式双环骨架产物。此外，本文还展示了产物的若干衍生转化以及桥联多环结构的一锅法制备。最后，密度泛函理论（DFT）计算表明，反应的对映选择性由初始的烯烃插入步骤决定，而环张力则调控了整体的区域选择性，更有利于5,6-双环产物的生成。