Experimental evidence for a [2 + 2] mechanism in the Lewis acid-promoted formation of α,β-unsaturated esters from ethoxyacetylene and aldehydes. Synthesis and characterisation of 4-ethoxyoxetes.

Abstract

4-Ethoxy-2H-oxetes 3a–c were prepared from ethoxyacetylene and alkoxy aldehydes 1a–c through MgBr₂–Et₂O promoted [2 + 2] cycloaddition reaction and were characterized at room temperature; their synthesis, which could occur via the formation of a chelate, establishes cycloaddition as the initial step in the formation of α,β-unsaturated esters 4a–c.