Photochemical rearrangements of stable silenes

Abstract

deep purple (the color of Fp2). We could not detect any other organic products.Preparation of Enolate Complexes 6c,d and 8c,d. 1,3-Dioxolanes (acetals) of -halo ketones were prepared by the published method.32 NaFp or Na/KFp* (10 mmol) in THF (10 mL) was added to a THF solution (20 mL) of appropriate 1,3dioxolane (12 mmol) at -78 °C. After the mixture was stirred for 3 h at room temperature, the volatiles were removed under reduced pressure. The product was extracted with ether (100 mL) and filtered through silica gel. The acetal linkage was hydrolyzed by stirring with 1/10 N HCl(aq), and then the organic layer was dried over MgS04. 6 and 8 were isolated by column chromatography followed by recrystallization from Et^O. 6c: 50% yield. 6d: 48% yield; yellow prisms; mp 90 °C. Anal. Caled for

Silenes: Connectors between classical alkenes and nonclassical heavy alkenes

“…The 29 Si NMR chemical shift for the 1,1-disilylsubstituted silenes 5a-5e vary in the range of 41-54 ppm (Table 1) [83,84], which is comparable to the 29 Si chemical shift of the parent silene (53.8 ppm according to high-level ab initio calculations [15]). This suggests that the Me 3 Si group resembles hydrogen when it comes to its effect on 29 Si NMR chemical shifts of silenes.…”

Polysilane Dendrimers

“…For example, reaction of LiMe with 7 and 10, respectively, generates after 2-3 days the highly air-and moisture-sensitive branched lithium silanides Li-18 [70,71] and Li-19 [72] ( Figure 4). Similarly, branched polysilane 21 [73] can be converted into Li-22 [74] in good yields ( Figure 5).…”

Acyl Silanes

“…The tris(trimethylsilyl)silyl ('sisyl') lithium reagent is prepared by deprotonation of tris(trimethylsilyl)silane using an alkyl lithium reagent. The related alkyl bis(trimethylsilyl)silyl lithium species have been prepared by several methods (Scheme 7) 26 . The silyl lithium reagents, which are yellow to orange to brown in colour, can be remarkably stable; for example, phenyl bis(trimethylsilyl)silyl lithium forms a recrystallizable pale yellow solid 'ate' complex with THF with the stoichiometry Ph(Me 3 Si) 2 SiLiÐ3THF.…”

“…The acyl silane unit is thus acting as a formal geminal diradical species. An interesting development of this reaction includes a stannyl group at the halo-(or xanthate-) bearing carbon atom, cyclization of an˛-stannyl radical then resulting in formation of an˛-stannylated silyloxy radical, from which the stannyl unit is lost, providing a regiospecific synthesis of cyclic silyl enol ethers (Scheme 86) 200 Cycloaddition reactions of acyl silanes appear to be rare, but Brook has shown that˛-silyloxy bis(trimethylsilyl)silenes (52), generated photochemically from acyl tris(trimethylsilyl)silanes (vide infra, Section IV.A.4), undergo [2 C 2] and [4 C 2] cycloaddition reactions with ketones, and [4 C 2] cycloaddition reactions with less bulky acyl silanes, as illustrated in Scheme 87 17,24,26,72,73,201 …”

“…Many of the silenes are remarkably stable and even recrystallizable 17,24,26,72,73 . They may undergo head-to-head or head-to-tail [2 C 2] dimerization to give 1,2-or 1,3-disilacyclobutanes, dependent upon the nature of the alkyl groups present 26 , and, while˛-silyloxy bis(trimethylsilyl)silenes (52) do not cycloadd to their parent acyl tris(trimethylsilyl)silanes, they do cycloadd to less bulky acyl silanes (Scheme 87) 202 . The structures of several 1,3-disilacyclobutanes have been determined by X-ray crystallography 201 Acyl silanes react readily in alcoholic solution upon near-visible irradiation 203 .…”