Efficient Asymmetric Synthesis of 2,6‐Disubstituted 2<i>H</i>‐Dihydropyrans <i>via</i> a Catalytic Hetero‐Diels–Alder/Allylboration Sequence

Abstract

Abstract [4+2] Cycloaddition of ( E )‐3‐borylacrolein 1 with ethyl vinyl ether, catalysed by chromium complex (1 R ,2 S ) or (1 S ,2 R ) 2 , led to the corresponding cycloadducts with high diastereo‐ and enantioselectivities. Further reaction with aldehydes offers an attractive asymmetric route to synthetically useful substituted 3,4‐dihydro‐2 H ‐pyrans.