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[摘要]：Dichloro- and phenylchlorocarbene (CCl2 and PhCCl) add to cyclooctyne via a barrierless process (MP2/6-311+G*, B3LYP/6-311+G*, B3LYP/6-31G*) to yield the expected corresponding cyclopropene adducts. A three-dimensional potential energy surface (PES) for CCl2 addn. to cyclooctyne (B3LYP/6-31G*) shows the formation of the cyclopropene product and also possible formation of a vinylcarbene. Residing in a shallow energy well, the vinylcarbene easily rearranges to the cyclopropene product, or to an exocyclic vinyl bicyclo[3.3.0]octane. Although the calcd. three-dimensional PES indicates possible dynamic control of the cyclooctyne-chlorocarbene system through the putative formation of a vinylcarbene (in addn. to the expected cyclopropene), addnl. calcns. and preliminary exptl. work show paths through the vinylcarbene to be unlikely. If the addns. of chlorocarbenes to cyclooctyne are controlled by reaction dynamics, we predict that the vast majority of the reactions proceed via traditional carbene cycloaddn. with only a very minor amt. of products formed from the alternative pathway. |
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