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43.3.1.2.3 Method 3: [2+2]-Cycloaddition Reactions

DOI: 10.1055/sos-SD-043-00126

Gilchrist, T. L.Science of Synthesis, (200843194.

The addition of alkenes to benzyne leads to the formation of benzocyclobutenes among other products.[‌2‌] Because of the electrophilic nature of benzyne, the [2+2] cycloaddition should show a greater degree of success with nucleophilic alkenes; however, the reaction occurs not only with enol ethers[‌227‌] and enamines,[‌228‌] but also with a wide range of other alkenes, including those such as ethyl acrylate, acrylonitrile, or methyl vinyl ketone that carry electron-withdrawing groups.[‌229‌,‌230‌] Although these reactions provide a direct entry to benzocyclobutenes, they have found relatively few synthetic applications because the yields of the cycloadducts are usually low and the cycloaddition is not stereoselective. Other reactions, particularly ene reactions (see Section 43.3.1.2.4), often compete with [2+2] cycloadditions.

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8-(eeee-Meeeeeeeeeeeeeeeeee)-8-eeeeee-8-eeeeeeeeeeeeee[8.8.8]eeee-8,8,8-eeeeee (888):[‌888‌]

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