New cross-aldol reactions. Reactions of silyl enol ethers with carbonyl compounds activated by titanium tetrachloride

Pyrrolidine-Mediated Direct Preparation of (E)-Monoarylidene Derivatives of Homo- and Heterocyclic Ketones with Various Aldehydes

“…Accordingly, the development of an efficient catalyst for the direct preparation of the monoarylmethylidenes of various homo-and heterocyclic ketones is a challenge and has become a much attempted sought after endeavor. As an alternative, mild Lewis acid-catalyzed tandem Mukaiyama aldol-dehydration reactions have been described [25][26][27], but silylation of the ketone introduces another step and reduces the atom economy [28]. To overcome this limitation, recent improved approaches employing different catalytic system have been reported [29][30][31][32].…”

Rac-(2R*,3R*)-S-Ethyl-4-Chloro-3-Hydroxy-2-Phenylbuthanethioate and Rac-(2R*,3R*)-S-Ethyl-2-Phenyl-3-(tosyloxy)buthanethioate: Dichotomy of the Stereoselectivity of the Mukaiyama Reaction

“…We have been exploring the scope and applicability of a pyrrole synthesis based on the two step sequence Mukaiyama cross-aldol reaction [6], followed by the Staudinger reaction [7,8]. To assemble the key elements, we have studied the Mukaiyama crossed aldol reaction between the silyl enol ether of S-ethyl 2-phenylethanethioate and simple aldehydes, like 2-chloroacetaldehyde (Scheme 1) and acetaldehyde (Scheme 2).…”

Notes on the directed aldol synthesis and reduction of some compounds related to cycloheximide

“…A general synthetic procedure leading regio-and stereospecifically to the requisite P-hydroxyketone functionality was sought, since the previous methods we used were not as simple and direct as we had hoped. We began by examining the TiC14-promoted directed aldol condensation procedure, initially described by T. Mukaiyama et al (2), to develop an efficient strategy for the synthesis of additional analogues whereby the cyclohexane ring substituents and (or) the imide ring portion of the molecule could be varied before introducing the P-hydroxyketone system. Recently, S. Kudo et al (3,4) used titanium and tin halide mediated methods to prepare optically active tratzs-cycloheximide isomers and chiral cis-cycloheximide isomers for antimicrobial activity studies.…”

“…The lack of high stereoselectivity was not surprising since Can Mukaiyama et al (2) and Heathcock et al (10) have reported Lewis acid catalyzed aldol condensations to give poor diastereoselectivity. Nonetheless, the preferential formation of some isomers might ensue (2) when steric hindrance is encountered between the trimethylsiloxy group of the cyclohexene and a substituent at position 6.…”