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The Stereochemistry of the Thermal Cheletropic Decarbonylation of 3-Cyclopentenone As Determined by Multiphoton Infrared Photolysis/Thermolysis

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posted on 2003-06-21, 00:00 authored by Gregory R. Unruh, David M. Birney
There are two allowed pathways for the thermal cheletropic decarbonylation of 3-cyclopentenone. The stereochemistry of decarbonylation of an unconstrained derivative (trans,trans-2,5-dimethyl-3-cyclopentenone, 4) has been determined for the first time. Under conventional pyrolysis conditions, thermal rearrangements of the initial product (trans,trans-2,4-hexadiene, 5) occur at the high temperatures required for the decarbonylation. However, by using multiphoton infrared photolysis/thermolysis to initiate decarbonylation, it was shown that the initial products from thermal decarbonylation of 4 are solely carbon monoxide and stereospecifically 5. The stereochemistry of decarbonylation is thus disrotatory, in accord with prior theoretical studies. A survey of crystal structures reveals ground-state distortions along this reaction coordinate as well.

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