Silacyclobutanes synthesis

With l,3>5-cycloheptatriene 2 can be trapped to yield four isomeric [2+2] adducts and the exo/endo isomeric [6+2] compound 16. Heating this mixture to 110°C leads to the complete transformation of the silacyclobutanes into 16 via a dipolar intermediate. The attempted synthesis of the diphenyl derivative of the [2+2] products leads to the stereospecific formation of endo-Yl which could be characterized by X-ray diffraction analysis [4]. 

Ring expansion in conjunction with Tamao-type oxidation of carbon-silicon bonds provides access to 1,4-diols. The l-(l-iodoalkyl)-l-silacyclobutanes are available from 1-chlorosilacyclobutanes (addition of vinyl, Scheme 34) <1991TL6383>. The utility of silacyclopentanes formed by the ring expansion of SCB for the synthesis of diols has been reported <1992TL7031, 1995BCJ625>. 

The synthesis and crystal structure of a complex containing a l-hafna-3-silacyclobutane ring was described <02OM1912>. 

This scheme was also used for the synthesis of a venlafaxine analogue containing a four-membered silacycle instead of a six-membered ring but Si-C bond cleavage with silacyclobutane ring opening took place in the amination step (Scheme 4) (04OM4987). 

Because of the close relationship between silicon and carbon, many attempts have been made to try to synthesize species containing multiple bonds to silicon (Si=C, Si=0, Si=Si, etc.). However, it was not until 1967 that compelling evidence was presented that Si=C might exist in the thermal reaction of 1,1-dimethyl-1-silacyclobutane (equation 90). The first evidence for the existence of Si=Si as transient intermediate was provided in the thermolysis of bridged disilane derivatives (equation 91). Since then, many studies have been published on these unsaturated species, but it was in 1981 that synthesis and characterization of relatively stable crystalline compounds containing Si=C (silene) (equation 92) and Si=Si (disilene) (equation 85) were reported (equations 90-92). 

Synthesis of 1,3-Disilacyclobutanes, 1,3-Digermacyclo-butanes, and l-Germa-3-silacyclobutanes with New 1,3-Dimetallated Organoelement Building Blocks... 

There is no synthetic route available for selective synthesis of unsymmetrically substituted 1,3-disilacyclobutanes, l-germa-3-silacyclobutanes, or 1,3-digermacyclobutanes. 

C. Strohmann, E. Wack, "Synthesis of 1,3-Disilacyclobutanes, 1,3-Digermacyclobutanes and I-Germa-3-silacyclobutanes with New 1,3-Dimetallated Organoelement Building Blocks" in Organosilicon Chemistry III From Molecules to Materials (Eds. N. Auner, J. Weis), Wiley-VCH, Weinheim, 1997, this volume p. 217. 

In order to obtain more reliable structural data on silaethenes with unstabilized Si=C double bonds, we tried to obtain the mmw spectrum of the parent species 3a. Contrary to the synthesis of substituted silaethenes such as 3b, the thermolysis of the corresponding silacyclobutane (4) proved to be less useful for obtaining the parent species 3a (route A in Scheme 6.1 1 ). 

Abstract The presented paper is a summary of our results on synthesis and polymerization of silyl-containing norbomenes and norbomadienes via ring-opening metathesis polymerization (ROMP) and addition processes as well as ring-opening polymerization (ROP) of silacyclobutanes and disilacyclobutanes. The synthesis of heterochain and carbochain polymer families with regularly varied substituents at Si atom and various number and location Si(CH3)3-substituents has been realized. Systematic study of gas transport parameters of polycarbosilanes series of different classes allowed us to find out real eorrelations between features of chemical polymer structure and its gas separation eharacteristics. 

Molecular design and precision synthesis of silicon-containing polymers are described. Polymerizations of substituted silacyclobutanes by phenyllithium and platinum complexes gave poly(carbosilane)s of head to tail regular structure. However, extensive chain transfer seems to have occurred in the polymerization by platinum complexes. 

The ROP of all known saturated SCHs proceeds via the rupture of endocyclic Si-C bonds. In the US patent issued in 1958, the first attempt was made to use a 4-membered SCH for the synthesis of heterochain PCSs [2]. From the late 1950s to the early 1980s, Vdovin and co-workers intensively investigated a new class of polymers - high-molecular-weight heterochain PCSs, prepared by the ROP of 4-membered SCHs - dimethyl-silacyclobutane (MSCB), tetramethyl-disilacyclobutane (DSCB) and their derivatives (see Sects. 1.1 and 1.2). The energy and structural characteristics of silacyclobutanes were analyzed in [3-10]. Though these publications are rather old, their results remain valid up to the present time. 

Ushakov NV, Fedorova GK, Finkelshtein ESh (1995) Synthesis and polymerization of Si-substituted silacyclobutanes. Izv Acad Nauk Ser Khim 2 2475-2477... 

Ushakov NV, Pritula NA, Rebrov A1 (1993) Synthesis and polymerization of 9-carbazolyl-containing 1-silacyclobutane derivatives. Russ Chem Bull 42 1372-1376 [translated from (1993) Izv Acad Nauk Ser Khim 8 1437-1441]... 

Matsumoto K, Miyagawa K, Matsuoka H, Yamaoka H (1999) Synthesis and solution behavior of the silicon-containing amphiphilic block copolymer, polystyrene-b-poly(3-hydroxymethyl-silacyclobutane. Polym J 31 609-613... 

Alekhin NN (1975) Investigation of polymerization of 1,1-dimethyl-1-silacyclobutane in the presence of alkali-metal silanolates, alkoholates, and alkatis. Ph D Thesis Academy of Sciences of the SSSR Topchiev Institute of Petrochemical Synthesis, Moscow... 

Hyun J-Y, Kawakami Y (2004) Silacyclobutane as Carbanion pump in anionic polymerization. III. Synthesis of di- and tri-block copolymer by diphenylsilacyclobutane-potassium tert-butoxide system. Polym J 36 856-865... 

Synthesis of Benzyl 2-Silyl-2-diazoacetates. Bolmetal. synthesized benzyl 2-dimethylthexylsilyl-2-diazoacetate from benzyl 2-diazoacetate with TDSOTf in the presence of ethyldiiso-propylamine in Et20 in 86% yield after column chromatography (eq 20). In contrast to other benzyl 2-silyl-2-diazoacetates, an attempt to prepare the corresponding benzyl 2-dimethylthexyl-silyl-2-oxoacetate via rhodium-catalyzed reaction of benzyl 2-dimethylthexylsilyl-2-diazoacetate with propylene oxide failed because of steric hindrance, forming a silacyclobutane via intramolecular C-H insertion reaction. 

Substituted silacyclobutanes can be prepared as a cisftrans isomeric mixture from t-, S-, or n-butyl-lithium and vinylalkoxysilanes. Substitution occurs with MeLi or PhLi. a-Silyl carbanions provide the intermediate for the stereoselective synthesis of tetrasubstituted alkenes with all four substituents different [equation (46)]. They can be readily desilyated using BrCN-AlQ or I [equation (47)], while the adduct formed between RLi and a-substituted vinylsilanes will itself attack SOa to give the sulphine [equation (48)]. ... 

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