Electrocyclic Reactions of Siloles: A Combined Experimental and Theoretical Study

Abstract

The reaction of 4-chloro-1,2-dimethyl-4-supersilylsila-1-cyclopentene (2 a) with Li[NiPr2] at -78 °C results in the formation of the formal 1,4-addition product of the silacyclopentadiene derivative 3,4-dimethyl-1-supersilylsila-1,3-cyclopentadiene (4 a) with 2,3-dimethyl-4-supersilylsila-1,3-cyclopentadiene (5 a). In addition the respective adducts of the Diels-Alder reactions of 4 a+4 a and 4 a+5 a were obtained. Compound 4 a, which displays an s-cis-silacyclopentadiene configuration, reacts with cyclohexene to form the racemate of the [4+2] cycloadduct of 4 a and cyclohexene (9). In the reaction between 4 a and 2,3-dimethylbutadiene, however, 4 a acted as silene as well as silacyclopentadiene to yield the [2+4] and [4+2] cycloadducts 10 and 11, respectively. The constitutions of 9, 10, and 11 were confirmed by NMR spectroscopy and their crystal structures were determined. Reaction of 4-chloro-1,2-dimethyl-4-tert-butyl-4-silacyclopent-1-ene (2 c) with KC8 yielded the corresponding disilane (12), which was characterized by X-ray crystal structure analysis (triclinic, P1). DFT calculations are used to unveil the mechanistic scenario underlying the observed reactivity.

Tetrakis(2,3,5,5-tetramethylhexen-2-yl)silane

“…Very recently, we have investigated the reaction of Si 2 Cl 6 with NR 3 (R = Me, Et) and we have been able to show that amine-complexed dichlorosilylenes represent the key intermediates in this disproportionation reaction (Meyer-Wegner et al, 2011). In the course of these studies we isolated along with SiCl 4 the [4 + 1] cycloadduct of dichlorosilylene SiCl 2 with 2,3-dimethyl-1,3-butadiene (DMB) in good yield upon treatment of Si 2 Cl 6 with catalytic amounts of NMe 3 or NMe 2 Et in neat DMB (Meyer-Wegner et al, 2014). In this study we report on the reaction of Si 2 Cl 6 with catalytic amounts of NMe 2 Et in the presence of DMB.…”

Unexpected Silaazetidine Formation in the Thermolysis of thf‐Supported Silanimine Et2Si=N–SitBu3·thf

“…[2] Thermal salt elimination (1,2-elimination of MX; M = alkali metal; X = halogens or other good leaving groups), which occur often at temperatures below -100°C [2] has preferably been used for the synthesis of reactive silenes. [2,25] As shown in Scheme 1, silanimines can be prepared (i) by a "Staudinger"-like reaction [6,26] of the silanides Na[SiRtBu 2 ] (R = tBu, Ph) [27,28] with tBu 2 SiClN 3 , (ii) by thermally [19,20,29] or CF 3 SO 3 SiMe 3 -induced [30] LiX elimination of halosilyl amides, (iii) by ring opening of silatetrazolines, [31][32][33] and (iv) by reaction of silylenes with azides [7,[9][10][11][12][13][14][15][16]22,34] . Furthermore, it is possible to gain access to silanimine [35] or silene [36] via [2+2] cycloreversion from 2-silaazetidine derivatives (cf.…”

Depolymerization of Cellulose and Synthesis of Hexitols from Cellulose Using Heterogeneous Catalysts

“…A number of synthetic routes towards silenes were reported 2. Thermal salt elimination (1,2‐elimination of MX ; M = alkali metal; X = halogens or other good leaving groups), which occur often at temperatures below –100 °C2 has preferably been used for the synthesis of reactive silenes 2,25…”