Synthesis and Thermal Reactivity of Enyne Allene Esters. An Intramolecular [2+2] Cycloaddition as a New Mode of Cycloisomerization

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Abstract
Enyne allene esters 4 and 5 were prepared under mild conditions using a Pd-catalyzed cross coupling reaction as the key step. Upon heating in the presence of 1,4-cyclohexadiene, 5 gave naphthalenes, while 4, in an unprecedented mode of cycloisomerization, was found to intramolecularly undergo a [2+2] cycloaddition leading to benzofulvene derivative 9.