Synthesis of benzocycloheptene-based amino acid derivatives via a [4+2] cycloaddition reaction as a key step

The seven-membered diene 5 is prepared from 2-butyne-1,4-diol using double orthoester Claisen rearrangement reaction as a key step. The Diels–Alder reaction of the diene 5 with various dienophiles followed by oxidation delivered the benzocycloheptene-based α-amino acid derivatives in very good yields.