Vinylsilanes preparation

Vinylsilane Preparation. The most general utility of the title reagent (1) involves Peterson alkenation reactions. Deprotonation of this reagent, followed by addition to carbonyl-containing substrates, affords phenylthiovinylsilanes (eq 1). ... 

The ( )-vinylsilane 151 was prepared by treatment of the silylstannation product 150 with hydrogen iodide[75] and the silylzincation product with water[70]. The silylstannylation of 1-ethoxyacetylene proceeds at room temperature using Pd(OAc)i and 1,1,3,3-tetramethylbutyl isocyanide regioselec-tively and an Si group is introduced at the ethoxy-bearing carbon. Subsequent Cul- and Pd-catalyzed displacement of the stannyl group in the product 152 with allyl halide, followed by hvdrolvsis, affords the acylsilane 153[79],... 

In Scheme 10, HMG-CoA reductase inhibitor 92 was synthesized via a Suzuki coupling approach. Hiyama s group also carried out a Hiyama coupling to make the same compound (93TL8263). Vinylsilane 119 was prepared by platinum-catalyzed reaction from terminal alkyne 89. 

For the preparation of divinyl ketones, as required for the Nazarov reaction, various synthetic routes have been developed. A large variety of substituted divinyl ketones, including vinylsilane derivatives, can thus be prepared. The Nazarov cyclization, and especially the vinylsilane variant, has found application for the synthesis of complex cyclopentanoids. 

The Ireland-Claisen reaction of ( )-vinylsilanes has been applied to the stereoselective synthesis of syn- and c/nti-2-substituted 3-silyl alkcnoic acids. a R-2-Alkyl-3-silyl acids are prepared by rearrangement of ( )-silyl ketene acetals which are generated in situ from the kinetically formed (Z)-enolate of the corresponding propionate ester40. Chelation directs the stereochemistry of enolization of heteroelement-substituted acetates in such a way that the syn-diastereomers are invariably formed on rearrangement403. 

These alkene isomers are separately available (4) by treatment of threo-S-trimethylsilyloctan-4-ol, prepared by reduction of the corresponding ketone with DIBAL in pentane at —120°C, with base or acid. The preparation of 5-trimethylsilyloctan-4-one itself illustrates three general procedures the addition of alkyl lithium reagents to vinylsilanes to generate a-lithiosilanes, the preparation of complex /5-hydroxysilanes, as diastereoisomeric mixtures, and the oxidation of such compounds to /8-ketosilanes... 

The cross metathesis of vinylsilanes is catalyzed by the first-generation ruthenium catalyst 9. This transformation has been extensively investigated from both preparative and mechanistic points of view by Marciniec et al. [86]. Interestingly, the same vinylsilanes obtained from cross metathesis may also result from a ruthenium-hydride-catalyzed silylative coupling and there might be some interference of metathesis and nonmetathesis mechanisms [87]. 

Entry 5 is an example of use of an a-trimethylsilylallyl group to prepare a vinylsilane. The stereochemistry is consistent with a cyclic TS having the trimethylsilyl substituent in a quasi-axial position to avoid interaction with the bridgehead hydrogen of the bicyclic ring. 

E)-Alkenylsilanes and -sulfides.2 Dibromomethyltrimethylsilane (1), prepared from ClSi(CH3)3 and CH2Br2, is reduced by commercial CrCl2 in THF to a reagent that converts aldehydes into (E)-vinylsilanes. A related reaction provides (E)-vinyl sulfides selectively from C6H5SCHC12. 

CYCLOHEXEN-l-ONE. Importantly, only 1.6 equivalents of Ag20 are required for efficient coupling. The final preparation in this series illustrates the hydrosilation of racemic 3-butyn-2-ol catalyzed by a phosphine based platinum(O) catalyst. The resultant racemic (E)-vinylsilane is then resolved with a commercially available lipase and subjected to a Johnson ortho ester Claisen rearrangement to afford [3R- AND 3S-]-(4E)-METHYL... 

The three-step procedure described for the preparation of the illustrated crotylsilanes is initiated with the hydrosilation of rac-3-butyn-2-ol. This procedure is significantly improved with respect to the positional selectivity of the hydrosilation resulting in exclusive formation of the racemic (E)-vinylsilane, and as a result the present procedure is much more amenable to scale-up than those previously described in the literature.8 The enzymatic resolution of the racemic secondary allylic alcohol (vinylsilane) has also been reported using commercially available lipase extracts. The use of a Johnson ortho ester Claisen rearrangement affords the (E)-crotylsilanes 4 in nearly enantiomerically pure form. 

Iminium ion-vinylsilane cyclizations closely related to the one described here have been used to prepare indolizidine alkaloids of the pumiliotoxin A and elaeokanine families, indole alkaloids, amaryllidaceae alkaloids, and the antibiotic (+)-streptazolin. The ability of the silicon substituent to control the position, and in some cases stereochemistry, of the unsaturation in the product heterocycle was a key feature of each of these syntheses. 

Stannylalumination of l-alkynes proceeds smoothly[7l], Silylstannation of l-alkynes with 144 proceeds to give 145 with high rcgio- and stereoselectivity. The reaction is cis addition and Sn always adds to the internal position. The addition products are converted into either a vinylsilane or a 2-stannylalk-ene[72-76]. The 2-stannylalkenc 146 is prepared by silylstannation of alkynes, followed by treatment with tributylammonium fluoride[77]. Rapamycin has been synthesized applying the silylstannation as a key step. The ew-adduct... 

Lithium aluminum hydride-Hexa-methylphosphoric triamide, 159 Methoxyamine, 177 Titanium(III) chloride-Diisobutyl-aluminum hydride, 303 Trimethylsilyl chlorochromate, 327 From vinylsilanes m-Chloroperbenzoic acid, 76 Miscellaneous methods to prepare ketones... 

The reaction exhibits excellent stereocontrol in most instances, with the major exception being simple alkenes. The reaction has been improved so that even these latter substrates give the desired products, by initial preparation of vinylsilanes (equation 5)40. The reaction occurs in good yields and the MesSi group can be easily removed at the end of the synthetic sequence. 

Dihydropyrans of general structure 110 can be prepared by two complementary strategies starting from aldehyde 113 (or its synthetic equivalent). Condensation with vinylsilane 114 or allylsilane 115 affords in each case the adduct 110 (Scheme 13.41). 

Overman and Blumenkopf prepared various seven- to nine-membered rings starting from vinylsilane 238 which was condensed with various acetals (Scheme 13.86) [56, 98, 99]. The desired medium-sized rings were obtained in moderate to good yields. 

Vinylsilanes are proper compounds which have won great appreciation as facile intermediates for many sorts of application. They are prepared either by addition reactions of acetylenes (vide supra) or by elimination reactions of saturated organosilanes. The main reactions, carried out with vinylsilanes, are addition reactions to obtain saturated organosilanes or electrophilic substitutions of the silyl group under Friedel-Crafts conditions where a rapid cleavage of the silyl moiety occurs (Scheme 8). 

This can be illustrated by the acylation of linear56,58) and cyclic57 vinylsilanes. It is quite simple to prepare methylvinylketone (59)56 or l-methyl-6-TMS-hexa-2,5-diene-4-one (70)58. In the latter case the starting material is bis(trimethylsilyl)-ethene (62) which can either be achieved via hydrosilylation (vide supra)30 or by the more classical approaches59-61. Furthermore, because of the high stereospecifi-ty, compounds like E- cinnamaldehyde (71) are obtainable in good yields and with superb optical purity62. ... 

Vinylsilanes and allylsilanes are prepared by dehydrogenative silylation of alkenes catalysed by Rh and other complexes [221]. A particularly effective catalyst for alkenylsilanes is Ru3(CO)12 [222], Using excess 1-hexene, 1-silyl-1-hexene 575 was... 

Alkylation of the corresponding dianion of acid 32 was very convenient and led to numerous 9-alkyl products. For example, analogue 58 was prepared via the LDA-generated dianion of 32, which was alkylated with f-butyl bromoacetate to provide acid-ester 64. Crude vinylsilane 64 was submitted to successive ozone addition and acidification. The resultant tetracyclic peroxide 65 was subsequently treated with trifluoroacetic acid to cleave the f-butyl ester to the free the acetic acid appendage of target 58 in 20% overall yield from 64 (Eq. 15). 

Other racemic analogues 166,167, and 169 were similarly prepared as shown in Scheme 13, to examine the effects of systematic variation on the lactone ring in these readily made analogues. For example, vinylsilane acid 188 was carefully... 

A novel application of dimethylsulfonium methylide for the general preparation of non-readily accessible and synthetically valuable 1-substituted vinylsilanes and styrene derivatives has been developed.55 It has been found that by varying conditions, the reactions can be tuned in either direction to give an alkene or cyclopropane exclusively. 

The divergent epoxide stereoisomers are available via epoxidation of the (E)- or (Z)-vinylsilanes, which in turn are prepared by (1) addition of an (/. )-vinyl Grignard reagent to the chlorosilacyclobutane, or (2) partial hydrogenation of an alkynylsilacyclobutane, respectively (Scheme 37). 

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