The Triplex Diels-Alder Reaction: An Investigation of Enantioselectivity and Scope
Part I. Enantioselective triplex Diels-Alder reaction. An investigation of the enantioselective triplex Diels-Alder reaction has been performed with optically active biaryl sensitizers, (-)1,1$\sp\prime$bis(2,4-dicyanonaphthalene) and (-)1,1$\sp\prime$bis(2,10-dicyanoanthracene). Irradiation of an optically active sensitizer in non-polar solvents containing substituted trans-$\beta$-methylstyrenes and cyclic dienes yielded endo (4+2) adducts with enantioselectivity up to 23%. Our report is the first observation of an enantioselective photochemical cycloaddition reaction which is catalyzed by a chiral sensitizer. The mechanistic investigation suggests the presence of diastereomeric exciplexes. The advantages and limitations of the reaction are discussed along with the results from the mechanistic study. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)
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