The direct and photosensitized photolysis of six methylated-1-pyrazolines is described. Examination of the products suggests that direct photolysis leads to ari excited singlet trimethylene, whereas a triplet is produced on benzophenone photosensitization. The trimethylene produced from 4 and 5 is related to the intermediates produced on addition of triplet methylenes to cis-and trans-2-butene. Evidence is presented to support the claim that no intermediate is involved in the addition of singlet methylene to cisand tratu-2-butene.
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