Formation of Cyclobutene Derivatives by -Cycloaddition

The [2+2] cycloaddition of acetylenes with alkenes remains to be the main pathway to cyclobutene derivatives [439], Theoretically, this 

The reaction of acetylene 4.978 with ethyl vinyl ether proceeds readily at 0°C, but the cyclobutene is unstable and undergoes spontaneous ring cleavage to form l-ethoxy-2-(trifluoroacetyl)-3-chloro-1,3-butadiene 4.984, and no other isomers or alkynylation products. l-Chloro-2-ethoxyoxalylacetylene is less reactive with vinyl ethers. Condensed cyclobutenes 4.985 and 4.986 were isolated by chromatography in moderate yield (Figue 4.2). 

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