The Mechanism ofthe Cycloaddition of SubstitutedKetenes to Cyclopentadiene Based on the Bent Bond/Antiperiplanar HypothesisOrbital Model

The [2 + 2] cycloaddition of substituted ketenes with cyclopentadiene producing bicyclo[3.2.0]­hept-2-en-6-ones is rationalized by the Bent Bond/Antiperiplanar Hypothesis (BBAH) orbital model. With monosubstituted ketenes, the <i>endo</i> isomer is formed preferentially. The <i>endo</i> and <i>exo</i> isomers are both produced with the cyclobutanone ring in the <b>co-folded in</b> conformation. Computational results support the analysis of the BBAH based mechanism in agreement with experimental results.