Reinvestigation on the Reaction of 2,6-Di-tert-butylbenzoquinone Methide and 2,6-Di-tert-butylphenol

Article abstract of DOI:10.1021/jo00027a053

The reaction of quinone methide 1 and phenol 2 in equimolar amounts was investigated in pentane at 30 deg C.Products were isolated by means of column chromatography on SiO2.There was a marked difference in product distribution between the reactions in the presence and absence of added Et3N.Dienones 3 and 10 were obtained only from the former reaction, while formation of 1,2-bis(4-hydroxyphenyl)ethane 18 and 4,4'-dihydroxybiphenyl 20 was overwhelming in the latter reaction.Other products from both reactions were relatively small quantities of 4,4'-stilbenequinone 17, 4,4'-diphenoquinone 21, and bis(4-hydroxyphenyl)methane 24, but dienone 4 was not obtained.Compounds 20 and 24 obtained from the latter reaction were formed by isomerization of dienones 19 and 23, respectively, during chromatography.The reaction is initiated by dimerization of 1 to generate biradical 11.Subsequent processes involving hydrogenation-dehydrogenation, coupling-dissociation, and dienone-phenol rearrangement account for the formation or the lack of formation of the products.The difference in product distribution is ascribed to capability of Et3N to catalyze the isomerization.Quinone methide 1 also adds to 2 to give 23.The decay of 1 in the presence of both 2 and phenol 6 gave dienone 8 additionally.The formation of 24 and 4 was facilitated by conducting the reaction of 1 and 2 in DMSO.Dehydrogenation of 10 and 3 with PbO2 afforded spirodienones 27 and 28, respectively.Compounds 27 and 28 were unstable, and their decay in solution was investigated in the presence or absence of added 2.The results show that the decay is initiated by homolytic scission of the C-C bond connecting the dienone rings in the cyclopentane (in 27) and cyclohexane (in 28) rings.Compound 28 is novel in that it bears two kinds of such C-C bonds.Reversibility of the dimerization of 1 is suggested.