Formal [4+2] cycloaddition of di-tert-butyl 2-ethoxycyclobutane-1,1- dicarboxylate with ketones or aldehydes and tandem lactonization

Abstract

A catalytic amount of tin(IV) chloride catalyzed formal [4+2] cycloaddition reaction of di-tert-butyl 2-ethoxycyclobutane- 1,1-carboxylate with ketones or aldehydes to give diethyl 6-ethoxydihydro-2H-pyran-3,3(4H)-dicarboxylates, whereas two equivalents of trimethylsilyl triflate promoted tandem [4+2] cycloaddition and lactonization to afford 3-oxo-2,6- dioxabicyclo[2.2.2]octane- 4-carboxylate esters. © 2012 The Pharmaceutical Society of Japan.