Mechanistic and exploratory organic photochemistry. 96. New photochemical rearrangement. Cyclopropyl-.pi.-methane rearrangement

Abstract

The photochemistry of 3-(2,2-diphenylcyclopropyl)-3-methyl-l ,I-diphenyl-1-butene was investigated in order to ascertain the reactivity of a system having one T moiety and one cyclopropyl ring attached to a saturated carbon. Only the singlet excited state proved reactive. As photochemical products there were obtained 1 ,I-diphenylethylene, 2-methyl-1 ,l-diphenyl-I-propene, 1 , I -diphenylbutadiene, 4-methyl-l,l-diphenyl-l,3-pentadiene, and 3-(2,2-diphenylvinyl)-2,2-dimethyl-1,l-diphenylcyclobutane. The cyclobutane product was considered as a potential reaction intermediate in the formation of the other products, and its photochemistry was investigated. Irradiation of the cyclobutane was found to afford 2-methyl-1,l -diphenyl-1 -propene and 1 ,l-diphenyl-1,3-butadiene but no diphenylethylene or 4-methyI-1,l-diphenyl-1,3-pentadiene. This evidence required that the diphenylethylene and the 4-methyl-1,l -diphenyl-l,3-pentadiene be primary photolysis products of the cyclopropylvinylmethane. Furthermore, extrapolation of the product distribution to zero time revealed an initial absence of 2-methyl-1,l-diphenyl-1-propene and diphenylbutadiene, thus showing these to be secondary photoproducts deriving from reaction of the cyclobutane. One a priori mechanism for formation of diphenylethylene and 4-methyl-1,l -diphenyl-1,3-pentadiene was carbene fragmentation followed by rearrangement. This was ruled out by independent study of the behavior of the carbene generated thermally and photochemically. A mechanism is postulated accounting both for formation of these products and the cyclobutane. This mechanism parallels that of the ubiquitous di-r-methane rearrangement but leads instead to the cyclobutane. Diversion of the reaction mechanism along the reaction coordinate leads to the fragmentation products.

Reactions involving electron transfer. 10. The use of .beta.-cyclopropyl .alpha.,.beta.-unsaturated ketones to detect anion radical intermediates

“…The mother liquors from this fractional crystallization were subjected to preparative liquid chromatography (silica gel with 1.5% Et20 in hexane as an eluent) to separate early fractions containing the unconjugated ketone 30 and later fractions containing the conjugated isomers 16. Fractional crystallization of these latter fractions from pentane at -70 °C separated an additional 228 mg of the enones 16 (total yield 852 mg or 56%): ir (CCU) 1675 (conjugated C=0) and 1595 cm-1 (conjugated C=C);23 uv max (95% EtOH) 264 nm (c 11 900) and 330 (shoulder, 168); NMR (CC14) 6.37 (t, J = 2.0 Hz, vinyl CH of minor stereoisomer) and 6.1-6.3 (m, vinyl CH of major stereoisomer, total 1 H), 2.0-3.2 (2 H, m, allylic CH2 including an apparent triplet of doublets, J = 2.0 and 6.5 Hz, at 2.70 shown by decoupling to be the allylic CH2 group of the minor stereoisomer), and 0.4-2.0 (19 H, m, aliphatic CH including a t-Bu singlet at 1.09); mass spectrum m/e (rel intensity) 192 (M+, 9), 177 (8), 138 (33), 135 (50), 107 (60), 93 (38), 91 (50), 79 (100), 77 (39), 57 (65), 41 (98), and 39 (66). Analysis by GLC (Apiezon M on Chromosorb P) exhibited partially resolved peaks with retention times of 9.7 (major) and 11.0 min (minor) corresponding to the two stereoisomers tentatively assigned structures 16b and 16a, respectively.…”

Stereochemistry of Carbenic 1,2-Vinyl Shifts

“…2,2-Dimethyl-1-phenyl-3-penten-1-one Tosylhydrazone (29). Following a method similar to the preparation of 11, 2,2-dimethyl-1-phenyl-(E)-4-penten-1-one ( 28) 13 (2.5 g, 13.3 mmol) and p-toluenesulfonylhydrazine (2.5 g, 13.5 mmol) afforded 3.1 g (65%) of (E)-29: mp 104 °C; 1 H NMR (CDCl3) δ 1.1 (s, 6 H), 1.5 (dd, J ) 6, 1 Hz, 3 H), 2.4 (s, 3 H), 5.15 (dq, J ) 16, 6 Hz, 1 H), 5.25 (dq, J ) 16, 1 Hz, 1 H), 6.7-7.8 (m, 9 H). Anal.…”

“…In previous sudies, vinyl shifts were induced by decomposition of the diazo compounds 4 (R ) Ph, Me). 6,7 Intramolecular C-H insertion (f6) and, in the case of R ) Ph, addition to π bonds were found to compete with vinyl migration (f5). These reactions are not well-suited for mechanistic analysis as the substrates 4 lack geometric isomerism, and spin inversion of the intervening allylcarbenes is presumed to be slow.…”

Synthetic protocols for the key functionalizations of the photochromic dihydroazulene scaffold

“…A few other dihydroazulene compounds bearing different groups from cyano at C1 should be mentioned here in the introduction. [18][19][20][21] They are mainly 1-phenyl, 1,1-diphenyl or 1,1-dimethyl-3-phenyl derivatives, and in only one example there was evidence of a photo-switching event (Scheme 2). 20 Compound 3 underwent a 1,3-sigmatropic arrangement upon irradiation, furnishing the isomer 4.…”