TY - JOUR
T1 - Competitive 1,2- and 1,5-hydrogen shifts following 2-vinylbiphenyl photocyclization
AU - Lewis, Frederick D.
AU - Sajimon, Meledathu C.
AU - Zuo, Xiaobing
AU - Rubin, Michael
AU - Gevorgyan, Vladimir
PY - 2005/12/9
Y1 - 2005/12/9
N2 - The photocyclization of 2-vinylbiphenyl and its derivatives has been proposed to occur via a two-step mechanism: photocyclization to form an unstable 8a,9-dihydro-phenanthrene intermediate, followed by exothermic unimolecular isomerization to a 9,10-dihydrophenanthrene. The mechanism of the hydrogen shift process has been investigated using deuterated derivatives of 2-isopropenylbiphenyl and 2,6-diphenylstyrene. 1H NMR analysis of the photoproducts indicates that the thermally allowed 1,5-hydrogen or deuterium shift is a minor product-forming pathway and that an unusual double 1,2-hydrogen or deuterium shift is the major product-forming pathway. The potential energy surface for photocyclization and hydrogen shift processes has been explored computationally. The calculated barrier for the 1,5-shift is predicted to be significantly lower than that for the 1,2-shift. Alternative mechanisms for the occurrence of 1,2-hydrogen or deuterium migration are presented.
AB - The photocyclization of 2-vinylbiphenyl and its derivatives has been proposed to occur via a two-step mechanism: photocyclization to form an unstable 8a,9-dihydro-phenanthrene intermediate, followed by exothermic unimolecular isomerization to a 9,10-dihydrophenanthrene. The mechanism of the hydrogen shift process has been investigated using deuterated derivatives of 2-isopropenylbiphenyl and 2,6-diphenylstyrene. 1H NMR analysis of the photoproducts indicates that the thermally allowed 1,5-hydrogen or deuterium shift is a minor product-forming pathway and that an unusual double 1,2-hydrogen or deuterium shift is the major product-forming pathway. The potential energy surface for photocyclization and hydrogen shift processes has been explored computationally. The calculated barrier for the 1,5-shift is predicted to be significantly lower than that for the 1,2-shift. Alternative mechanisms for the occurrence of 1,2-hydrogen or deuterium migration are presented.
UR - http://www.scopus.com/inward/record.url?scp=28744455778&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=28744455778&partnerID=8YFLogxK
U2 - 10.1021/jo051730y
DO - 10.1021/jo051730y
M3 - Article
C2 - 16323856
AN - SCOPUS:28744455778
SN - 0022-3263
VL - 70
SP - 10447
EP - 10452
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
IS - 25
ER -