Mukayama-aldol reaction

Scheme 32 Unsaturated aldehydes, ketones and esters in the hydroformylation/Mukayama aldol reaction...

The Mukayama-aldol reaction, which runs under the severe conditions of hydroformylation, ends up with a complete migration of the silyl group. With this methodology, particularly spirocyclic aldol adducts, hydropentalenes, hydroindanes, or substituted naphthols become available. 

Li, H. J., Tian, H. Y., Chen, Y. J., Wmg, D. and Li, C. J., Novel chiral galhum Lewis acid catalysts with semi-crown ligands for aqueous asymmetric Mukayama aldol reactions, Chem. Commurt, 2002, 2994 2995. 

Successful examples of the Mukayama aldol reaction include the use of the thermally stable tris(pentafluorophenyl)borane Lewis acid. Yamamoto and coworkers reported that 2 mol% of (C6Es)3B smoothly catalyzes the Mukaiyama-aldol reaction of various silyl enol ethers or ketene silyl acetals with aldehydes (Equation 45). ... 

All investigations on the use of Lewis acids in the hetero Diels-Alder reaction of carbonyl compounds clearly show that a careful adjustment of the Lewis acidity for a given system is neccessary. Especially with trimethylsilyloxybuta-dienes a Mukayama type aldol reaction can easily take place instead of the desired hetero Diels-Alder reaction. 

The above solid catalysts were used successfully to catalyze various reactions, like the Suzuki-Miyura reaction [15], such as aminocarbonylation, amidatimi, and the Heck reactions [16]. Polymers containing scandium trillate, ruthenium, platinum, or gold were prepared to perform Mukayama aldol, alcohol, and sulfide oxidation, hydrogenatirMi, and indole syntheses [17]. 

Hereupon, the cyanosilylation of aromatic aldehydes and ketones, as well as the Mukayama aldol condensation, which is more sensitive to acidity (this reaction requires stronger Lewis acid sites than cyanosilylation), become feasible. In the presence of the Mn-MOF, a pronounced molecular-sieve effect is observed, which correlates well with the size of pores. This manifestation of the substrate size selectivity indicates the occurrence of the true heterogeneous catalysis. 

In 2001, Rychnovsky and co-workers completed the synthesis of the leucascandrolide macrolactone. The key features of the Rychnovsky s synthesis are the Mukayama aldol-Prins cascade reaction of alkyl enol ether with the aldehyde forming 2,6-cij-tetrahydropyran, and Hosomi-Sakurai allysilane addition to generate 2,6-tranj-tetrahydropyran (Schemes 2.12, 2.13). 

A full paper on the synthesis of octoses by the "naked sugar" approach has been published (see Vol.23, Chapter 2, ref.31). An improved, shorter version of this synthesis employs a Wittig Homer reaction instead of the original Mukayama cross-aldolization for chain-extension. Similar work has been reported by a Japanese group. ... 

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