Synthesis of cyclobutane serine analogues.

In this paper, we describe a thermal [2 + 2] cycloaddition involving 2-acylaminoacrylates as electron-poor acceptor alkenes, a reaction that involves a Michael-Dieckmann-type process. The reaction gives rise to a new substituted cyclobutane skeleton that can be transformed into amino acid derivatives. For example, a number of transformations were carried out to give the two pairs of stereoisomers of the 2-hydroxycyclobutane-alpha-amino acid serine analogue (c(4)Ser); compounds 22 and 23. This synthesis covers a gap in knowledge in the broad field of restricted amino acids.