Silanes enoxy

Cu(II) and Sn(II) Bisoxazolinc Complexes. Evans has prepared and studied a family of Cu(II) complexes prepared from bisoxazoline ligands [8]. Utilizing these complexes a number of different addition reactions can be successfully conducted on pyruvate, benzyloxyacetalde-hyde, and glyoxylates. Whereas the focus of the work in the context of aldol addition reactions has been on the use of silyl ketene acetals (vide infra), the addition of ketone-derived enoxy silanes 8a-b with methyl pyruvate has been examined (Eq. 8B2.1). The additions of 8a-b proceed in the presence of 10 mol % Cu(II) catalyst at -78°C in CH2Cl2, affording adducts of acetophenone 9a and acetone 9b with 99% and 93% ee, respectively. 

Moreover, the formation of enoxy-silanes via silylation of ketones127 by means of N-methyl-N-TMS-acetamide (1 72) in presence of sodium trimethylsilanolate (173) was reported in 1969 and since then, the use of silylating reagents in presence of a catalyst has found wide appreciation and growing utilization as shown in recent papers128-132 (Scheme 27). Diacetyl (181) can be converted by trifluoromethylsul-fonic acid-TMS-ester (182) into 2,3-bis(trimethylsiloxy)-l, 3-butadiene (7treatment with ethyl TMS acetate (7 5)/tetrakis(n-butyl)amine fluoride l-trimethylsiloxy-2-methyl-styrene (i<56)130. Cyclohexanone reacts with the combination dimethyl-TMS-amine (18 7)/p-toluenesulfonic acid to 1-trimethylsiloxy-l-cyclohexene (iSS)131. Similarly, acetylacetone plus phenyl-triethylsilyl-sulfide (189) afford 2-triethylsiloxy-2-pentene-4-one (790)132. ... 

Enoxy silanes Lewis acid (equiv.) Products Isolated yields (P/aat C-10)... 

The pioneering discovery by Mukaiyama in 1974 of the Lewis acid mediated aldol addition reaction of enol silanes and aldehydes paved the way for subsequent explosive development of this innovative method for C-C bond formation. One of the central features of the Mukaiyama aldol process is that the typical enol silane is un-reactive at ambient temperatures with typical aldehydes. This reactivity profile allows exquisite control of the reaction stereoselectivity by various Lewis acids additionally, it has led to the advances in catalytic, enantioselective aldol methodology. Recent observations involving novel enol silanes, such as enoxy silacyclobutanes and O-si-lyl M(9-ketene acetals have expanded the scope of this process and provided additional insight into the mechanistic manifolds available to this versatile reaction. 

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