Aldehydes, p-siloxy

Epoxy Silyl Ether MABR P-Siloxy Aldehyde Yield (%)... 

Rh catalyses the hydrosilylation of alkenes and the dehydrogenative silylation of 1,5-dienes and alkynes, and the silylcarbonylation of alkynes to give p-silylacrylaldehydes with exceptional stereocontrol , ketones and enones give silyl enol ethers, 1,3-cyclobutane dione gives 3-hydroxycyclobutanone, and assists in the silylformylation of ethynyl pyirolidone derivatives to give pyrrolizidine alkaloids, and epoxides to give p-siloxy aldehydes, and... 

The optically active aldol products derived from a- or P-siloxy aldehydes with the tetra-substituted ketene silyl acetals were successfully transformed to the anti-aldol compounds by Guindon s stereoselective defunctionalization method [67] as depicted in Scheme 10.43 [68]. 

Maruoka K, Ooi T, Yamamoto H. Organoaluminum-promoted rearrangement of epoxy silyl ethers to p-siloxy aldehydes. J. Am. Chem. Soc. 1989 111 6431-6432. 

Reaction with dimethylphenylsilane is catalyzed at room temperature under 250 psi of carbon monoxide. Other silanes tested, triethyl- and triphenylsi-lane, are not effective reagents in this system. A variety of aldehydes are good substrates for the reaction, including benzaldehyde, substituted benzaldehydes, and heterocyclic aldehydes. Aliphatic aldehydes also yield a-siloxy aldehyde products, but the reaction must be run at higher CO pressure (1000 psi) to avoid hydrosilylation. The reaction does not tolerate substrates bearing strong electron-withdrawing substituents, such as p-nitrobenzaldehyde. 

A recent example has been described by Brown et al. who have studied the KR of p-nitrophenyl esters of the d- and i-N-tert-butoxycarbonyl derivatives of glutamine and phenylalanine with ethanol or methanol promoted by chiral lanthanide complexes, providing enantioselectivities of up to 99% ee [302]. On the other hand, an enantioselective hydrolysis of phenylalanine derivatives was reported in 1986, providing a perfect enantiomer discrimination (s> 1000), as a result of catalysis with a tripeptide [303]. In 2007, Maruoka et al. reported the KR of differently a,a-disubstituted a-siloxy aldehydes based on an asymmetric rearrangement into the corresponding chiral acyloins using axially chiral organoaluminium Lewis acids, which provided selectivity factors of up to 39.5... 

Yamaoka Y, Yamamoto H (2010) Super silyl stereo-directing groups for complete 1,5-syn and -anti stereoselectivities in the aldol reactions of p-siloxy methyl ketones with aldehydes. J Am Chem Soc 132 5354... 

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