Mukaiyama coupling

A variety of alkyl pyridinium salts have been used in the Mukaiyama coupling a representative example is shown below. 

The acceptor for the projected 3-1-3 coupling was prepared from fluoro-donor 134 and lactal 132 (Scheme 23). Compound 127 was readily converted to lactal acceptor 132, while 134 was prepared from selectively protected galactal 133. It seemed prudent to convert 133 to the more reactive p-derivative 134 by direct opening of the epoxide with TBAF, followed by protection of the resultant hydroxyl. Mukaiyama coupling of 132 with 134 proved troublesome. While the yield was high (72%), the major impediment was selectivity (a P, 3 1). The desired... 

In 1989, Isayama and Mukaiyama reported a related Co-catalyzed coupling reaction that employs a,b-unsaturated nitriles, amides, and esters with PhSiLb as a hydrogen source [9]. Cobalt-bis(diketonato) complex, Co(II)(dpm)2 [dpm = bis(dipivaloylmethanato)] (5mol%), exhibited high catalytic activity at 20 °C in the coupling of excess acrylonitrile and ben-zaldehyde to provide b-hydroxy nitrile 4 in 93% yield (syn anti = 50 50) (Scheme 5). N,N-Dimethylacrylamide and methyl cinnamate both reacted... 

As described above, our synthetic strategy involves the convergent construction of the central cyclopentanone ring with a carbonylative cross-coupling reaction and a photo-Nazarov cyclization reaction (Chart 2.2). The electrophilic coupling component 51 was synthesized by an intramolecular Diels-Alder reaction [34] and the nucleophilic coupling component 52 by a vinyiogous Mukaiyama aldol reaction [35]. 

Thus, Mukaiyama [30] introduced the TiCU-Zn couple, which gives good results with aromatic aldehydes and ketones, but not with the corresponding aliphatic derivatives ... 

Aldol and Related Condensations As an elegant extension of the PTC-alkylation reaction, quaternary ammonium catalysts have been efficiently utilized in asymmetric aldol (Scheme 11.17a)" and nitroaldol reactions (Scheme ll.lTb) for the constmction of optically active p-hydroxy-a-amino acids. In most cases, Mukaiyama-aldol-type reactions were performed, in which the coupling of sUyl enol ethers with aldehydes was catalyzed by chiral ammonium fluoride salts, thus avoiding the need of additional bases, and allowing the reaction to be performed under homogeneous conditions. " It is important to note that salts derived from cinchona alkaloids provided preferentially iyw-diastereomers, while Maruoka s catalysts afforded awh-diastereomers. 

Analysis of the Mukaiyama-type aldol coupling (Eq. 2) and the well-known hydrosilyla-tion of a,/l-unsaturated carbonyl compounds 11 in the presence of a rhodium catalyst, indicate that both can be explained by the intervention of the rhodium enolate 13. This line of reasoning provided the impetus to develop a new crossed aldol coupling using a hydrosilane, an a,yS-unsaturated ketone 11, and an aldehyde to form 15 (Scheme 6.4). 

For a review of coupling reactions of acetals, sec Mukaiyama Murakami Synthesis 1987, 1043-1054. For a discussion of the mechanism, see Abell Massy-Wcstropp Aust. J. Chem. 1985, 38. 1031. For a list of substrates and reagents, with references, see Ref. 508, pp. 404-405. 

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