Selenophen‐2‐yl‐Substituted Thiocarbonyl Ylides – at the Borderline of Dipolar and Biradical Reactivity

Abstract

The reactions of aryl (selenophen-2-yl) thioketones with CH2N2 occur with spontaneous elimination of N2, even at low temperature (-65°), to give regioselectively sterically crowded 4,4,5,5-tetrasubstituted 1,3-dithiolanes and/or a novel type of twelve-membered dithia-diselena heterocycles as dimers of the transient thiocarbonyl S-methanides. The ratio of these products depends on the type of substituent located at C(4) of the phenyl ring. Whereas the formation of the 1,3-dithiolanes corresponds to a [3 + 2] cycloaddition of an intermediate thiocarbonyl ylide with the starting thioketone, the twelvememberd ring has to be formed via dimerization of the 'thiocarbonyl ylide' with an extended biradical structure.

Kinetic aspects of [3+2] cycloaddition reactions between (E)-3,3,3-trichloro-1-nitroprop-1-ene and ketonitrones

“…The mechanistic aspects of [3?2] cycloaddition reactions have recently drawn ever greater attention from organic chemists [1][2][3][4][5][6][7][8][9][10]. It turned out that in the case of reactions including strongly electrophilic dipolarophiles, a stepwise, zwitterionic mechanism may compete with a classical one-step mechanism.…”

A convenient access to 1,2-diferrocenyl-substituted ethylenes via [3 + 2]-cycloelimination of 2-silylated 4,4,5,5-tetrasubstituted 1,3-dithiolanes

“…> 158°C (decomp., from pentane/CH 2 Cl 2 ); yield: 420 mg (75%). 1 3086w, 2924w, 1645w, 1385w, 1250m, 1227m, 1103m, 1065m, 1039w, 999m, 925w, 837m (Z)-6b (minor product) was identified based on the spectra of a mixture of isomers: 1 H NMR (600 MHz, CDCl 3 ): δ 3.91 (s, 10CH(Fc)), 4.17 (brs, 8CH(Fc)), 6.84-6.88 (m, 2CH(Thi)) ppm. 13 Fc)), 87.7 (2C(Fc)), 124.0, 125.5, 126.7 (3 signals for 6CH(Thi)), 133.4, 145.6 (C = C, 2C(Thi)) ppm.…”

“…1:1 mixture of (E)-and (Z)-isomer. 1 10CH(Fc)), 4.25-4.26 (m, 4CH(Fc)), 4.34-4.35 (m, 4CH(Fc)) ppm. 13 Fc)), 133.6 (C = C).…”

“…In a series of recent publications, reactions of aryl/hetaryl thioketones 1 with diazomethane and its derivatives, such as diazoethane, 2-diazopropane and (trimethylsilyl)diazomethane, were reported [1][2][3][4]. The non-concerted pathway of the formal [ macrocyclic dimer of the intermediate thiocarbonyl S-methanide [1,5] as well as sterically crowded 4,4,5,5-tetrasubstituted 1,3-dithiolanes [2].…”

“…The non-concerted pathway of the formal [ macrocyclic dimer of the intermediate thiocarbonyl S-methanide [1,5] as well as sterically crowded 4,4,5,5-tetrasubstituted 1,3-dithiolanes [2]. The latter products were formed via trapping of the intermediate diradical species by the starting thioketones in a regioselective manner.…”