Access to Complex Scaffolds Through [2 + 2] Cycloadditions of Strained Cyclic Allenes

Abstract

We report the strain-induced [2 + 2] cycloadditions of cyclic allenes for the assembly of highly substituted cyclobutanes. By judicious choice of trapping agent, complex scaffolds bearing heteroatoms, fused rings, contiguous stereocenters, spirocycles, and quaternary centers are ultimately accessible. Moreover, we show that the resulting cycloadducts can undergo thermal isomerization. This study provides an alternative strategy to photochemical [2 + 2] cycloadditions for accessing highly functionalized cyclobutanes, while validating the use of underexplored strained intermediates for the assembly of complex architectures.

Diels–Alder Cycloadditions of Oxacyclic Allenes and α-Pyrones

“…We were interested in evaluating a related class of strained intermediates, cyclic allenes ( 6 , Figure ), in Diels–Alder cycloadditions with α-pyrones ( 4 ). Several factors motivated these studies: a) Similar to cyclic alkynes 3 , cyclic allenes 6 can be generated under mild reaction conditions and exhibit strain-promoted reactivity. ,,− b) Cyclic allenes 6 have two sites of reactivity that can be differentiated based on substituent effects, potentially allowing for the controlled formation of isomeric products. c) Like linear allenes, cyclic allenes 6 are chiral, providing long-term opportunities to control stereochemistry.…”