A Carbene Relay Strategy for Cascade Insertion Reactions.

Insertion reactions that involve stabilized electrophilic metallocarbenes are of great importance for installing α-heteroatoms to carbonyl compounds. Nevertheless, the limited availability of carbene precursors restricts the introduction of only a single heteroatom. In this report, we describe a new approach based on an I(III) /S(VI) reagent that promotes the cascade insertion of heteroatoms. This is achieved by sequentially generating two α-heteroatom-substituted metal carbenes in one reaction. We found that this mixed I(III) /S(VI) ylide reacts efficiently with a transition metal catalyst and an X-H bond (where X=O, N). This transformation leads to the sequential formation of a sulfoxonium- and an X-substituted Rh-carbenes, enabling further reactions with another Y-H bond. Remarkably, a wide range of symmetrical and unsymmetrical α,α-O,O-, α,α-O,N-, and α,α-N,N-subsituted ketones can be prepared under mild ambient conditions. In addition, we successfully demonstrated other cascades, such as CN/CN double amidation, C-H/C-S double insertion, and C-S/Y-H double insertion (where Y=S, N, O, C). Notably, the latter two cascades enabled the simultaneous installation of three functional groups to the α-carbon of carbonyl compounds in a single step. These reactions demonstrate the versatility of our approach, allowing for the synthesis of ketones and esters with multiple α-heteroatoms using a common precursor.