title: Viscosity-dependent diastereoselectivity and product selectivity in the photodenitrogenation of a spirocyclopropane-substituted, DBH-type azoalkane.
abstract: In the photodenitrogenation of the spirocyclopropane-substituted azoalkane 1 in alcoholic solvents of various viscosity (from 0.6 to 89.2 cP) to the diastereomeric housanes 2 (major product) and bicyclo[3.2.0]heptenes 3 (minor product), the same (within experimental error) viscosity dependence is observed in the diastereoselectivity of the housane 2 formation as well as in the product selectivity (2/3). These viscosity effects corroborate the intermediacy of the diazenyl diradical 1DZ as a common branching point for the housane 2 and bicycloheptene 3 formation. In contrast, the diastereoselectivity of the bicycloheptene 3 generation is independent of viscosity, which implies that a nitrogen-free, symmetrical 1,4 diradical serves as precursor to the rearrangement products. The free-volume model of viscosity is employed to rationalize the product selectivity as well as the diastereoselectivity.
authors.affiliation: Institute of Organic Chemistry, University of Wuerzburg, Am Hubland, D-97074, Wuerzburg, Germany. adam@chemie.uni-wuerzburg.de
authors.forename: Waldemar
authors.initials: W
authors.lastname: Adam
authors.forename: Meledathu C
authors.initials: MC
authors.lastname: Sajimon
authors.forename: Alexei V
authors.initials: AV
authors.lastname: Trofimov
mesh_terms: D000438:Alcohols / Q000737:chemistry; D000473:Alkanes / Q000737:chemistry*; D001391:Azo Compounds / Q000737:chemistry*; D003521:Cyclopropanes / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D010782:Photolysis; D013141:Spiro Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D014783:Viscosity
chemical_list: D000438:Alcohols; D000473:Alkanes; D001391:Azo Compounds; D003521:Cyclopropanes; D013141:Spiro Compounds; D009584:Nitrogen