4072-09-7Relevant academic research and scientific papers
Buttressing Effect in Carbene Chemistry. Effect of 3-Alkyl Groups on the Reactions of 2-Alkoxydiphenylcarbenes
Tomioka, Hideo,Kimoto, Kohji,Murata, Hiroshi,Izawa, Yasuji
, p. 471 - 477 (2007/10/02)
Irradiation of 2-methoxydiphenyldiazomethane 1a in diethyl ether at 10 deg C gave 3-phenyldihydrobenzofuran 3a along with a small amount of the ether adduct 4a, which became the major product when the irradiation was carried out in the ether matrix at -196 deg C.The reaction patterns were dramatically changed as an alkyl group was introduced into the 3-position of substrates 1.Thus, irradiation of 2-methoxy-3-alkyldiphenyldiazomethanes 1b-d in diethyl ether either at 10 deg C or at -196 deg C afforded the corresponding benzofurans 3b-d at the complete expense of the ether adducts 4b-d.The results are nicely explained in terms of the buttressing effect of the 3-alkyl group, which prevents the 2-methoxy group from lying in the plane of the phenyl ring in the precursor molecules and assists the methoxy group in rotating around the C-O bond toward the carbene centre after elimination of N2.Generation of carbenes 2 in methanol at 10 deg C produced O-H insertion adducts 5 as the major product at the expense of benzofurans 3.The ether 5a was formed as a major product in the reaction of carbene 2a with the alcohol matrix at -196 deg C, but the benzofurans 3 became the major product in the irradiation of substrates 1b-d in methanol matrix at -196 deg C.The results are again explicable in terms of the buttressing effect of 3-alkyl substituents on the relative populations of thew rotational isomers of the carbenes 2.The effect of the 3-alkyl group on the reaction of 2,2',5'-trimethoxydiphenylcarbenes 7 which form two kinds of intramolecular C-H insertion products 8 and 9 were studied and the results are again discussed in terms of the buttressing effect.
