Rhodium catalysis addition

The need for higher product specificity and milder reaction conditions (see also Section IX) has led to extensive research in hydroformylation technology. This research, as reported in technical journals, patent literature, and commercial practice has been primarily concerned with catalysis by rhodium, in addition to the traditional cobalt, and with catalyst modification by trialkyl or triaryl phosphines. These catalyst systems form the basis for the major portion of the discussion in this chapter some other catalyst systems are discussed in Section VIII. 

Carbon-carbon bond-forming reactions are one of the most basic, but important, transformations in organic chemistry. In addition to conventional organic reactions, the use of transition metal-catalyzed reactions to construct new carbon-carbon bonds has also been a topic of great interest. Such transformations to create chiral molecules enantioselectively is therefore very valuable. While various carbon-carbon bond-forming asymmetric catalyses have been described in the literature, this chapter focuses mainly on the asymmetric 1,4-addition reactions under copper or rhodium catalysis and on the asymmetric cross-coupling reactions catalyzed by nickel or palladium complexes. 

Overall, this book clearly illustrates what we can do in organic synthesis using rhodium catalysis and I have no doubt that it will serve as an excellent reference text for both graduate students and synthetic chemists at all levels in academia and industry. Moreover, I anticipate that this book will stimulate additional research in the area of organorhodium chemistry, and serve to inspire those involved in the development and application of new synthetic methodology. 

Direct C-H activation of 2-imidazolines in the addition to alkenes has been observed under rhodium catalysis as shown for the formation of 586 (Scheme 139) <20040L1685>. The proposed intermediate was thought to be similar to that involved in metal-N-heterocyclic carbene (NHC) complexes <2002AGE1290>. 

In enynes, both the double and the triple bond can compete for the carbenoid that is generated from alkyl diazoacetate under copper or rhodium catalysis. The chemoselectivity is sometimes not very pronounced, but but-l-en-3-yne is selectively attacked at the triple bond [methyl diazoacetate, RhjCOAc), 70% yield], whereas in 2-methylhexa-l,5-dien-3-yne only the double bonds accept the carbenoid (Table 12, entry 2). The vinylcyclopropene obtained by addition to the triple bond may dimerize to form a 3,6-dialkoxycarbonyltricyclo-[3.1.0.0 ]hexane.2 "... 

Another synthetic method for the production of pseudoionone, which starts from myrcene [94a], [94b], has never been commercialized for the production of fragrance materials (see also p. 45, geranylacetone). The process consists of a rhodium-catalyzed addition of methyl acetoacetate to myrcene, transesterification of the resulting ester with allyl alcohol, and an oxidative decarboxylation of the allyl ester under palladium catalysis to obtain pseudoionone. 

The rhodium-catalyzed addition of arylboronic acids to a, 3-unsaturated ketones was first reported by Miyaura in 1997 [44], and only a short time thereafter the first enantioselective addition was documented by Hayashi [45]. Excellent reviews are available that summarize the early developments in this rapidly expanding field of asymmetric catalysis [46] consequently, only recent advances wiU be included in this section. 

That Rh-allyl complexes can also act as nucleophiles in addition to aldehydes has been demonstrated by Oshima et al. in 2006 [198]. Retro-aUylation of the homoallyl alcohol 191 under rhodium catalysis generates a nucleophilic aUylrhodium species that reacts with aldehydes 190 to give the corresponding secondary alcohols 192 in situ (Scheme 12.94). Subsequent isomerization of these alcohols proceeds under the reaction conditions to furnish the corresponding saturated ketones 193 in modest to good yields. 

Scheme 3.14 Three-component tandem bicyclobutanation-homoconjugate addition-enolate trapping reaction catalysed by a combination of chiral rhodium catalysis and copper catalysis.

The conjugate addition of HSiR3 onto a, y -unsaturated ketones is of particular interest in synthesis. Silylenolates are thus easily obtained and can be further used. Cobalt catalysis has been recommended as a particularly convenient method for the preparation of such silylenolates [82]. Earlier reports refer to rhodium catalysis [82], and palladium and nickel [83] catalysts. 

Complex preparation Tandem catalysis access to ketones from aldehydes and arylboronic acids via rhodium-catalyzed addition/oxidation, (52%) [1628]. 

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