Regioselectivity rhodium-catalyzed

Evans and Kennedy later combined the regioselective rhodium-catalyzed allylic alkylation, using a-substituted malonates, with ring-closing metathesis for the construction of five-, six-, and seven-membered carbocycles (Scheme 10.2) [13]. The combination of these methodologies allowed for the rapid and flexible assembly of carbocycles possessing vicinal ternary-quaternary or quaternary-quaternary stereogenic centers. 

Tab. 10.3 The scope of the regioselective rhodium-catalyzed allylic alkylation with copper(l) enolates.

Tab. 10.6 The TolN(Li)Mbs. scope of regioselective rhodium-catalyzed allylic amination of carbonates with...

Tab. 10.7 Regioselective rhodium-catalyzed allylic etherification with ortfio-substituted phenols.

Tab. 10.8 summarizes the application of rhodium-catalyzed allylic etherification to a variety of racemic secondary allylic carbonates, using the copper(I) alkoxide derived from 2,4-dimethyl-3-pentanol vide intro). Although the allyhc etherification is tolerant of linear alkyl substituents (entries 1-4), branched derivatives proved more challenging in terms of selectivity and turnover, the y-position being the first point at which branching does not appear to interfere with the substitution (entry 5). The allylic etherification also proved feasible for hydroxymethyl, alkene, and aryl substituents, albeit with lower selectivity (entries 6-9). This transformation is remarkably tolerant, given that the classical alkylation of a hindered metal alkoxide with a secondary alkyl halide would undoubtedly lead to elimination. Hence, regioselective rhodium-catalyzed allylic etherification with a secondary copper(l) alkoxide provides an important method for the synthesis of allylic ethers. 

Slagt. V.F., van Leeuwen, P.W.N.M. and Reek, f.N.H. (2003) Midticomponent porphyrin assemblies as functional bidentate phosphite ligands for regioselective rhodium-catalyzed hydroformylation. Angew. Chem., Int. Ed., 42, 5619-5623. 

Selent D, Franke R, Kubis C, Spannenberg A, Baumann W, Kreidler B, Bomer A (2011) A new diphosphite promoting highly regioselective rhodium-catalyzed hydroformylation. Organometallics 30 4509 514... 

Scheme 1 Regioselective rhodium catalyzed hydroformylation of 75 in the presence of acylguanidinium containing ligand 76.

Scheme 5.17 Simplified mechanism for n-regioselective rhodium-catalyzed isomerization-hydroformylation.

Figure 5.10 Ligands for highly n-regioselective rhodium-catalyzed hydroaminomethylation of internal olefins.

Lautens, M. Yoshida, M. Regioselective rhodium-catalyzed addition of arylhoronic acids to alkynes with a pyridine substituted water soluble hgand. Org. Lett. 2002, 4, 123-125. 

Watkins AL, Landis CR. Regioselective rhodium-catalyzed hydroformylation of 1,3-dienes to highly enantioenriched beta, gamma-unsaturated aldehyes with diazaphospholane ligands. Org. Lett. 2011 13 164-167. 

Abstract Recent advances in synthetic aspects of the rhodium-catalyzed hydroformylation of alkenes are reviewed. Emphasis is given to practical improvements, efficient new catalysts for regioselective and enantioselective hydroformylation, and to applications of the reaction in organic synthesis. Furthermore, new developments in directed hydroformylation are covered as well as new approaches toward efficient hydroformylation catalysts employing the concept of self-assembly. 

Table 5 Regioselectivities of rhodium-catalyzed hydroformylation of 1-octene using toluene and MeOH as solventsa...

Diastereoselective syntheses of dihydrobenzo[f>]furans have been accomplished by a rhodium-catalyzed regioselective and enantiospecific intermolecular allylic etherification of o-iodophenols as a key step, providing the corresponding aryl ally ether 122, which leads to a dihydrobenzo[b]furan by treatment of the intermediate aryl iodide with tris(trimethylsilyl)silane and triethylborane at room temperature in the presence of air <00JA5012>. 

The rhodium-catalyzed cyclization/hydrosilylation of internal diyne proceeds efficiently with high stereoselectivity (Scheme 106). However, terminal diynes show low reactivity to rhodium cationic complexes. Tolerance of functionalities seems to be equivalent between the rhodium and platinum catalysts. The bulkiness of the hydrosilane used is very important for the regioselectivity of the rhodium-catalyzed cyclization/hydrosilylation. For example, less-hindered dimethylethylsilane gives disilylated diene without cyclization (resulting in the double hydrosilylation of the two alkynes), and /-butyldimethylsilane leads to the formation of cyclotrimerization compound. 

In order to account for the high regioselectivities observed in the rhodium-catalyzed hydroboration of styrenes, Hayashi proposed a modified mechanism which proceeds through 73-benzyl-rhodium complex 22 as a key intermediate (Scheme 7). Reductive elimination from this 73-benzyl-rhodium complex 22 produces the secondary alkylborane regioselectively.12 A related 73-benzyl-palladium complex was recently isolated by Hartwig in studies of hydroamination.75... 

Although early catalysts were based on cobalt, nowadays, rhodium catalysts are preferred because they require lower pressure and afford higher chemo- and regioselectivity [1,2]. In recent years, extensive research into the production of only linear aldehydes has provided impressive results. The application of phosphines with a wide bite angle in the rhodium catalyzed hydroformylation of terminal alkenes enable the regioselectivity to be almost totally controlled [3]. Branched selective hydroformylation, al-... 

For example, rhodium catalyzed hydroformylation of 2-formyl-N-allyl-pyrrol gives an approx. 1 1 mixture of iso- and u-aldehydes. The latter cyclizes immediately in an aldol reaction followed by dehydration giving 7-formyl-5,6-indolizine in up to 46% (Scheme 29) [83]. Since here only one of the aldehyde groups can act as the enolate nucleophile this cyclization proceed with high regioselectivity (Scheme 29). 

A moderate pressure (>5 atm.) of CO in the reaction system leads to the selective formation of 29, while alkynes undergo rhodium-catalyzed hydrosilylation with a hydrosilane to afford vinylsilanes in the absence of CO. The presence of the rhodium complex is crucial for the smooth progression of siiyiformyiation, regardless of the presence of mononuclear or polynuclear complexes. This generalization is supported by the studies of many others [15]. The most important feature of this reaction is the excellent regioselectivity, which favors the formylation of the internal sp-carbon of the acetylenic bond of terminal... 

It is possible to carry out the [2+2+2] cyclotrimerization reaction in a regioselective manner by using a partially or completely intramolecular approach. Rhodium-catalyzed intramolecular cyclotrimerization of 1,6,11-triynes, which construct fused 5-6-5 ring-systems, has been studied extensively [33-36]. Cyclization of 1,6,11-triyne 47 catalyzed by RhCl(PPh3)3, gives the tricyclic benzene 48 in good yield (Eq. 14) [33a]. 

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