Reductive silylation zinc chloride

The 1,4-reduction of a,/3-unsaturated aldehydes is best carried out with diphenylsilane in the presence of zinc chloride and tetrakis(triphenylphosphine) palladium436 or a combination of triethylsilane and tris(triphenylphosphine) chlororhodium 437 Other practical approaches use phenylsilane with nickel (0) and triphenylphosphine438 and diphenylsilane with cesium fluoride.83 It is possible to isolate the initial silyl enol ether intermediate from the 1,4-hydrosilylation of o, /3-unsaturated aldehydes (Eq. 264).73,411 The silyl enol ethers are produced as a mixture of E and Z isomers. 

Reductive coupling of carbonyls to alkenes Titanium(IV) chloride-Zinc, 310 of carbonyls to pinacols Titanium(III) chloride, 302 Titanium(IV) chloride-Zinc, 310 of other substrates Samarium(II) iodide, 270 Reductive cyclization 2-(Phenylseleno)acrylonitrile, 244 Tributylgermane, 313 Tributyltin hydride, 316 Triphenyltin hydride, 335 Trityl perchlorate, 339 Reductive hydrolysis (see Hydrolysis) Reductive silylation Chlorotrimethylsilane-Zinc, 82... 

Enzymatic 7-ACA splitting procedures [for general review, see 261] have been developed and commercialized by companies like Asahi Chemical, Hoechst, and Novartis. The replacement of the hitherto employed chemical deacylation processes like the imino ether (Figure 1.1-3) or the nitrosyl chloride method [262] resulted in a cost reduction of 80% and a decrease of the waste volume by a factor 100 from 311 to 0.3 tons per 1-ton 7-ACA. Chlorinated hydrocarbons like dimethyl aniline and methylene cloride as well as heavy metal ions can be completely avoided. Instead of zinc salt formation, multiple silylation, formation of the imino chloride, imino ether, and finally an imino ether hydrolysis, the side chain is removed in two enzymatic steps (Figure 1.1-3). 

Total syntheses of racemic muscarine and allomuscarine were achieved by Pirrung and DeAmicis 11), who used a new approach to formation of the stereoselectively substituted tetrahydrofuran nucleus (Scheme 8). The key step in this procedure was the stereospecific photochemical ring expansion of a cyclobutanone derivative. The cycloaddition of silyl enol ether with methylchloroketene generated by zinc dechlorination of 2,2-dichloropropionyl chloride followed by reductive removal of the halogen produced the methylsiloxycyclobutanone intermediate. Irradiation of the... 

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