3-Silyloxy esters

Silyloxy esters.l Silyl ketene acetals are known to undergo aldol condensation with carbonyl compounds in the presence of TiCl4 (12,268) to afford (3-silyloxy esters. The same products can be obtained in a one-step reaction of an a,p-unsaturated ester with trimethylsilane and a carbonyl compound in the presence of RhCl3H20. 

In the Mukaiyama cross-aldol reaction, an aldehyde and a ketene silyl acetal [e.g. (43)] react via Lewis acid catalysis to give a jS-silyloxy ester (44). The reaction... 

Homo-Reformatsky reaction.1 The reaction of 1-ethoxy-1-trimethylsilyloxy-cyclopropane (1) with an aldehyde in the presence of ZnCl2 results in y-silyloxy esters via a zinc homoenolate (a) of ethyl propionate (equation I). Znl2 is the preferred catalyst in the case of reactions with acetophenone and benzaldehyde dimethyl acetal and in reactions of l-isopropoxy-l-(t-butyldimethylsilyl-oxy)cyclopropane with aromatic aldehydes. 

In 2004, (3-lactams were obtained by the cyclization of (3-amino esters [231]. The treatment of the latter with 10% Pd-C in the presence of ammonium formiate for 3 h, followed by silylation of the resulting hydroxyl esters gave the silyloxy esters that were subjected to cyclization using the Breckpot reaction [232, 233] to give the (3-lactams (Scheme 106). 

Lithio ethyl acetate is prepared in quantitative yield by reaction of LHMDS with ethyl acetate in THF at —78 °C. Reaction with carbonyl compounds leads to condensation products in high yield (eqs 3 and 4). No racemization of the a-silyloxy esters occurs (eq 4). 

Our approach was based on the ring opening of fluoroalkyl p-lactams. These p-lactams can be obtained either through a [2+2] ketene-imine cycloaddition with a fluoroacetaldimine, or by the cyclocondensation of an alkoxy or silyloxy ester enolate on this same fluoroacetaldimine. The preparation of fluoroalkyl P-lactams 16 (Rf = CF3, CFjH and CF2CI) and the preparation of homochiral P-lactams and isoserines 14 and 15, have been have investigated with success by these two approaches. 

The reaLUons of phenyltetrafluorophosphorane with numerous silylated secondary or tertiary a- or (1-hydroxy esters, ketones, nitriles, ethers, nitro, and trichloromethyl derivatives have been investigated, the corresponding a or p fluoro derivatives are obtained in yields varying from reasonable to nearly quantitative [24, 25, 26, 27 The application of phenyltetrafluorophosphorane for fliiorination of silyloxy steroids has also been reported [28]... 

A type Ilae cyclocondensation of silyloxy enynes catalyzed by TMSOTf produced highly substituted pyrrole-2-acetic esters <06OL3881>. 

The a-silyloxy alkyl radical generated by the addition of (TMS)3Si radical to the aldehyde moiety of 45 has been employed in radical cyclization of (3-aminoacrylates (Reaction 7.53) the trans-hydroxy ester and the lactone in a 2.4 1 ratio were the two products [62]. 

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