# Palladium-catalysed asymmetric annulations of Morita–Baylis–Hillman carbonates with allenes or alkenes via migratory insertion

## TL;DR

A new palladium-catalyzed method enables efficient and selective synthesis of complex molecules using Morita–Baylis–Hillman carbonates and allenes or alkenes.

## Contribution

A novel catalytic strategy enables migratory insertion of non-zwitterionic π-allylpalladium intermediates for asymmetric annulations.

## Key findings

- π-allylpalladium intermediates from MBH carbonates isomerize and undergo migratory insertion into allenes and alkenes.
- The method forms (3 + 2) adducts with high regio- and stereoselectivity via a cascade of reactions.
- Density functional theory calculations provide mechanistic insights into the catalytic process.

## Abstract

As one of the most versatile intermediates in organic synthesis, π-allylpalladium complexes have been extensively exploited in allylic alkylation reactions with a wide range of nucleophiles. In contrast, their engagement in the migratory insertion process remains significantly underdeveloped. Here we demonstrate that the π-allylpalladium intermediates derived from Pd0 and Morita–Baylis–Hillman (MBH) carbonates of activated ketones can isomerize to the corresponding η1-form when stabilised by a pendent carbonyl group, and undertake migratory insertion into various allenes and even styrene-type alkenes efficiently. Subsequent vinylogous deprotonation of the newly formed multifunctional π-allylpalladium species followed by isomerization and intramolecular allylic alkylation leads to skeletally diverse (3 + 2) adducts with high levels of regio- and stereoselectivity. This catalytic strategy not only achieves migratory insertion of non-zwitterionic π-allylpalladium intermediates, but also overcomes the inherent limitations that the MBH carbonates can only undergo annulations with electrophilic dipolarophiles via Lewis base catalysis. Mechanistic insights are further elucidated through comprehensive density functional theory calculation studies.

The palladium-catalysed asymmetric (3 + 2) annulations of Morita–Baylis–Hillman carbonates with allenes and alkenes are reported via a cascade oxidative addition/migratory insertion/vinylogous deprotonation/isomerisation/allyllation sequence.