Crystal structure, computational study, and Hirshfeld analysis of exo-1,2,3,5-tetraphenyl-1a',9b'-dihydrospiro[bicyclo[3.1.0]hexane-6,1′-cyclopropa[l]phenanthren]-2-en-4-one

Abstract

The reaction of dibenzonorcarynyliden(e/oid) with phencyclone was recently reported to give a congested spiropentane with endo stereochemistry. Herein we report that, in sharp contrast, an analogous reaction using tetracyclone, instead of phencyclone, gives the highly crowded title spiropentane but with exo stereochemistry as determined by X-ray crystallography. This new tetracyclone adduct (C44H30O) crystallizes upon slow evaporation from hexanes/ethyl acetate in the monoclinic crystal system and P21/n (No. 14) space group. It has one molecule in the asymmetric unit and four molecules per unit cell. DLPNO-CCSD(T)/def2-TZVP//B3LYP/def2-SVP calculations indicate that the endo spiropentane diastereomers from phencyclone and tetracyclone are both more stable than the corresponding exo forms by 6.68 and 5.35 kcal mol−1, respectively. As noted previously in the phencyclone system, favorable π-stacking interactions between the two flat biphenyl moieties in the product and transition state may lead to the preferential formation of the endo diastereomer. However, the ability of the phenyl rings in the 3,4-position of the tetracyclone component to rotate could introduce destabilizing steric interactions in the transition state that hinder formation of the endo diastereomer in favor of the less thermodynamically stable exo isomer.

Keywords

• crystal structure
• spiropentane
• stereochemistry
• hirshfeld analysis