High pressure-promoted [2+2] cycloaddition reactions of 4-methylphenyl 1,2-propadienyl sulfone with enol ethers

Under high pressure conditions, 4-methylphenyl 1,2-propadienyl sulfone (1) and enol ethers (6) undergo regioselective [2+2] cycloaddition reactions to give (3-alkoxycyclobutylidene)methyl 4-methylphenyl sulfones (7). The cycloaddition reaction has a broad scope with respect to the substituents allowed at the enol ether. The synthetic potential of the obtained cycloadducts is illustrated by a stereoselective addition of dimethylamine to the double bond of 7a and 7b to yield 11a and 11b and by a tertiary amine-induced double bond isomerisation of 7a and 7b, followed by ring-opening of the cyclobutene intermediate to yield 1-alkoxybuta-1,3-dienes 12a and 12b.