PHOTOCHEMISTRY OF ISOPIPERITENONE AND 4-ACETOXYISOPIPERITENONE : An unprecedented photochemical reaction of an α &β unsaturated ketone*
Citation: Willum F. Erman and Thomas W. Gibson (1969/01/20) PHOTOCHEMISTRY OF ISOPIPERITENONE AND 4-ACETOXYISOPIPERITENONE : An unprecedented photochemical reaction of an α &β unsaturated ketone*. Tetrahedron,vol.25, page 2493 to 2515 (RSS)
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Tagged: Chemistry
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Summary
Objective: Photochemical analysis of isopiperitenone and 4-acetoxyisopiperitenone
When (+)-isopiperitenone and 4-acetoxyisopiperitenone are exposed to ultravoilet radiation using a Pyrex filter give (+)-1,2-dimethyltricyclo[3.3.0.0]octan-6-one in 35-42% yield and 5-acetoxy-1,2-dimethyltricyclo[3.3.0.0]octan-6-one in 42% yield. Mechanism involved in above two reaction is a noval cleavage of α,β unsaturated ketone.
Tricycloketone is produced by photochemical transformation of (+)-isopiperitenone. Intermediate involved in this reaction is a biradical species generated by the cleavage of α,β unsaturated ketone. The intermediate undergoes cyclization with alkene group present in above isopoperitenone . The asymmetric center is not affected in the above photochemical reaction and therefore final product will be optically active. In photocycloaddition reaction, stereochemistry and thermodynamic factors are important parameters. Orbital orientation of (+)-isopoperitenone facilitate a particular stereo product.
On exposing 4-acetoxyisopiperitenone in ultraviolet radiation form a 5-acetoxy-1,2-dimethyltricyclo[3.3.0.0]octan-6-one and yield of this reaction is slightly higher than other one (isopiperitenone). That is because in this reaction biradical is stabilized by acetoxy group. Intermediate involve in this reaction is similar to the isopiperitenone photocyclization reaction.
The formation of product by cleavage of bond between α,β and β,ϒ unsaturated ketone is novel and this type of reaction (photocycloaddition) is very rare in case of β,ϒ unsaturated allylic ketones.
