| Abstract
| - Thermal [2 + 2] cycloaddition of allenes with an additional multiple bond is described. By simply heatingthe allenenes or allenynes having a three-atom tether in an appropriate solvent such as dioxane or DMF,the distal double bond of the allenic moiety regioselectively participates in the cycloaddition to formbicyclo[4.2.0]oct-5-ene derivatives in good to excellent yields. In all the reactions of allenenes, the olefingeometry was completely transferred to the cycloadducts. While the reaction of terminal allenes affordedbicyclic cyclobutane derivatives as a single isomer, the cycloaddition of some internal allenes with axialchirality yielded a diastereomeric mixture of cycloadducts. These results are in good accordance withthe stepwise mechanism through a biradical intermediate with a coplanar allyl radical.
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