The reactions of several aryldiazomethanes (1a: p-tolyl; 1b: phenyl; 1c: p-chlorophenyl) with chloranil gave stilbenes (3) and spiro-oxetanes (4) at 20 °C in tetrahydrofuran or 1,2-dichloroethane. The isomer ratios of 3 were ca. 2 to 3:1 in favor of cis, depending on the solvents and on the substituents of 1. In the case of 4, however, stable trans-isomers were selectively formed. On the other hand
Solvent Effects in the Conversion of Phenyldiazomethane into Stilbene and Spirooxetane in the Reaction with Chloranil
作者:Takumi Oshima、Ryoji Nishioka、Toshikazu Nagai
DOI:10.1246/bcsj.55.904
日期:1982.3
aprotic solvents. The products were trans-spirooxetane(4) and cis-trans mixtures of stilbene(3) (ca. 2–5 times cis-rich). The molar ratios of cis-3 to the sum of the trans-3 and 4 tended to increase, whereas the 4 to trans-3 ratios decrease with the increase in the solvent basicity and polarity. These effects of solvents on the product distributions were interpreted in terms of the effects of the solvent
Oxetanes from [2+2] Cycloaddition of Stilbenes to Quinone via Photoinduced Electron Transfer
作者:Duoli Sun、Stephan M. Hubig、Jay K. Kochi
DOI:10.1021/jo981754n
日期:1999.4.1
The photochemical coupling of various stilbenes (S) and chloranil (Q) is effected by the specific charge-transfer (CT) activation of the precursor electron donor-acceptor (EDA) complex [S, Q], and the [2+2] cycloaddition is established by X-ray structure elucidation of the crystalline trans-oxetanes formed selectively in high yields. Time-resolved (fs/ps) spectroscopy reveals the (singlet) ion-radical pair (1)[S.+, Q(.-)] to be the primary reaction intermediate and thus unambiguously establishes for the first time the electron-transfer pathway for this typical Paterno-Buchi transformation. The alternative cycloaddition via the specific activation of the carbonyl component (as a commonly applied procedure in Paterno-Buchi couplings) leads to the same oxetane regioisomers in identical molar ratios. As such, we conclude that a common electron-transfer mechanism applies via the quenching of the photoactivated quinone acceptor by the stilbene donor to afford triplet ion-radical pairs (3)[S.+, Q(.-)] which appear on the ns/mu s time scale. The spin multiplicities of the critical ion-pair intermediate [S.+, Q(.-)] in the two photoactivation methodologies determine the time scale of the reaction sequences (which are otherwise the same), and thus the efficiency of the relatively slow ion-pair collapses (k(c) similar or equal to 10(8) s(-1)) to the 1,4-biradical that ultimately leads to the oxetane product.
Xu, Jian-Hua; Wang, Long-Cheng; Xu, Jian-Wei, Journal of the Chemical Society. Perkin transactions I, 1994, # 5, p. 571 - 578