Electronic Control of Stereoselectivity. 7. Stereospecificity of N-Methyltriazolinedione Cycloaddition to Tricyclo2,6>deca-2,5-diene, Tricyclo2,6>deca-2,5,8-triene, and Tricyclo2,6>undeca-2,5,8-triene

Article abstract of DOI:10.1021/jo01312a020

The Diels-Alder reactions of the title compounds (1-3) with N-methyltriazolinedione (MTAD) were investigated and determined to proceed with endo stereospecificity.Stereochemical assignment to the adduct derived from 3, viz., 4, was arrived at by a three-dimensional X-ray crystal structure analysis.In the case of 9, the cycloadduct derived from 2, reliance was placed upon diimide reduction of its more reactive internal double bond from the exo direction to give 10, hydrolysis-oxidation of which delivered the azo compound 12.Direct irradiation of this substance afforded cage compound 13, thereby demonstrating the close spatial proximity of C=C and N=N in the precursor molecule.The stereochemistry of the third and final adduct 14 was deduced by chemical interconversion with 9 and 11.The heightened reactivity of MTAD results in the development of early transition states where prevailing electronic factors are magnified.The overwhelming preference for endo stereoselection is attributed to important electronic effects which are present in strained bicyclo systems and can make themselves recognized at more distant sites in fused cyclopentadiene rings.