Rh(I)-Catalyzed [5 + 2]/[2 + 2] Cycloaddition Cascade to Access a Cyclobutane-Fused [4–5–6–7] Tetracyclic Framework

Abstract

A Rh(I)-catalyzed [5 + 2]/[2 + 2] cycloaddition cascade has been developed to afford a complex and highly strained [4−5−6−7] tetracyclic framework in good yields and excellent diastereoselectivities. During this transformation, three rings, three C−C bonds, and four contiguous stereocenters were formed efficiently. Mechanistically, the rare sterically congested multisubstituted cyclobutanes are constructed readily through Michael addition and a Mannich reaction cascade.

Recent updates on vinyl cyclopropanes, aziridines and oxiranes: access to heterocyclic scaffolds

“…The cyclobutane structural motif, which can be broadly described as a cyclobutane-type framework, is embedded in a significant and diverse array of natural products and biologically active molecules. 100 Recently, Wang and coworkers 101 developed a synthetic route to access a highly strained cyclobutane-fused [4–5–6–7] tetracyclic framework 154 via an intermediate 153 by an Rh( i )-catalyzed [5 + 2]/[2 + 2] cycloaddition reaction between vinyl aziridines 56 and dienones 152 (Scheme 51). The desired product 154 was obtained as a single diastereomer in a good yield (up to 96%) with excellent diastereoselectivity in the presence of catalyst Rh(COD)BF 4 at 0° C; hence, these were chosen as optimal reaction conditions for further studies.…”