From Acylsilanes

Silylfiirans are available from acylsilane dicarbonyl confounds <96JOC1140>. Fhotocycloaddition of 35 with aUcenes leads cleanly to tetrasubstituted furans 38 in yields of 85%. A mechanism is proposed involving an alkyl propargyl biradical (as 36) that closes first to a vinyl carbene (as 37) and than to 38 <96JOC3388>. 

The novel [6+2] annulation approach developed by the Takeda group has also been included in a threefold anionic/pericyclic process (Scheme 2.149) [340]. The reaction leads to functionalized eight-membered rings 2-659 in a highly stereoselective manner, starting from acylsilanes 2-656 and 3-(trimethylsilyl)vinyl-lithium (2-657). After 1,2-addition and 1,2-Brook rearrangement, the cyclobutane 2-... 

Addition of acyl anions generated from acylsilanes to a,(3-unsaturated ketones using N-heterocyclic carbenes (NHCs) derived from thiazolium salts as catalyst produced 1,4-diketones, which cyclized to form the corresponding furans in good yields under an acidic condition <06JOC5715>. 

The very different reactivity toward allylation of a,P-unsaturated esters and acyl-silanes [132] is due to stabilization of the allyl cation intermediates by the alkoxy group in the former class of substances, in contrast to those derived from acylsilanes which are expected to be less stable than 3-monooxyallyl cations. In the 1,1-dioxy substituted cations two donor atoms are bonded to the acceptor site, but in the 1-oxy-3 -silyl congeners a rf,a-antagonism (captodative) exists. 

Table 28 Synthesis of vinylsilanes from acylsilanes and PT-sulfones Barbier conditions at - 78 °C using LHMDS under...

Eijectron spin resonance spectra alkyls and aryls, 7, 173 anion radicals from acylsilanes, 7, 138 metal nitrosyls, 7, 234 phosphine methylenes, 9, 298 Elimination reactions, 7, 166-167 Exchange reactions ferrocenes, 10, 80, 91 organo-Group II compounds, 8, 170-176... 

Difluoroenoxysilanes. The synthesis from acylsilanes is promoted by Bu4N (Ph3Snp2). With BU4NF the primary products undergo further aldol reactions. 

Schemp 6,14 Stereoselective formation of a-suhstituted enol silyl ethers from acylsilanes and vinyl lithium.

Scheme fi.15 Formation of siloxyallenes from acylsilanes and alkynyllithinms. 

Scheme 6.30 Generation of [1-siloxy homoenolates from acylsilanes and amide enolates.

Hydrogen peroxide j sodium hydroxide Carboxylic acids from acylsilanes... 

Synthesis of sec. alcohols from acylsilanes via 1,1-hydroxysilanes Asym. induction... 

Brigaud and Portella et al. applied Yb(OTf)3 to aldol reaction of a,a-difluoroenol silyl ether (2) affording difluoromethylene ketones, a common structural motif of HlV-1 protease inhibitor [4], (2) was generated from acylsilane and trifluo-romethyltrimethylsilane and directly subjected to the aldol reaction with aldehydes with 10 mol% ofYb(OTf)3 in a one-pot procedure (Scheme 13.1). The same reaction with other Lewis acids such as TiCU or BF3-OEt2 required more than stoichiometric amount. 

Lettan, R. B. II, Woodward, C. C., Scheldt, K. A. (2008). Highly stereoselective synthesis of substituted y-lactams from acylsilanes. Angewandte Chemie International Edition, 47, 2294-2297. 

RfCH20SiMe3 with Ph3PICl gives RfCH2l, fluorinated butane and pentanediols give siloxanes with (Me3Si)2NH, and difluoroenoxysilanes result from acylsilanes and CF3SiMe3559. 

Siloxycarbene (88), easily generated from acylsilane (87) under microwave irradiation, is known to insert into the benzylic C-H bond to provide benzofuran (89) in a diastereoselective manner. DPT studies have provided insight into the mechanism... 

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