Alkenes enantioselective additions

The catalytic enantioselective addition of vinylmetals to activated alkenes is a potentially versatile but undeveloped class of transformations. Compared to processes with arylmetals and, particularly alkylmetals, processes with the corresponding vinylic reagents are of higher synthetic utility but remain scarce, and the relatively few reported examples are Rh-catalysed conjugate additions. In this context, Hoveyda et al. reported very recently an efficient method for catalytic asymmetric allylic alkylations with vinylaluminum reagents that were prepared and used in Thus, stereoselective reactions... 

In comparison with the platinum catalysts, rhodium catalysts are much more reactive to effect addition of bis(catecholato)diboron even to non-strained internal alkenes under mild reaction conditions (Equation (5)).53-55 This higher reactivity prompted trials on the asymmetric diboration of alkenes. Diastereoselective addition of optically active diboron derived from (li ,2i )-diphenylethanediol for />-methoxystyrene gives 60% de (Equation (6)).50 Furthermore, enantioselective diboration of alkenes with bis(catecolato)diboron has been achieved by using Rh(nbd)(acac)/(A)-QUINAP catalyst (Equation (7)).55,56 The reaction of internal (A)-alkenes with / //-butylethylene derivatives gives high enantioselectivities (up to 98% ee), whereas lower ee s are obtained in the reaction of internal (Z)-alkenes, styrene, and a-methylstyrene. 

In total, over the past six years, the chelating P,N-ligands have shown considerable promise in a variety of enantioselective processes, including transfer-hydrogenation and hydrosilylation of ketones, hydroboration of alkenes, conjugate addition to enones and Lewis-acid catalysed Diels-Alder reactions, in addition to those described above.128,341 It is anticipated that this list will continue to grow, and... 

An interesting enantioselective addition-allyl-transfer sequence of an electron-deficient alkene 163 with alkyliodides and allyltributylstannane 164 was described... 

The synthesis of lineatin, a pheromone of the insect Trypodendron lineatum, involves the enantioselective addition of methane to the double bond of alkene A in the presence of a chiral rhenium catalyst on silica (Re /silica see Figure 2.19). Michael performed eight separate experiments for this reaction in a 500 mL high-pressure stirred autoclave reactor using liquid methane as a solvent and 0.05 mmol catalyst. The results are shown in Table 2.2. 

The catalytic enantioselective addition of aromatic C - H bonds to alkenes would provide a simple and attractive method for the formation of optically active aryl substituted compounds from easily available starting materials. The first catalytic, highly enantioselective Michael addition of indoles was reported by Jorgensen and coworkers. The reactions used a,fl-unsaturated a-ketoesters and alkylidene malonates as Michael acceptors catalyzed by the chiral bisoxazoline (BOX)-metal(II) complexes as described in Scheme 27 [98,99]. 

Alkene Hydroarylation. The enantioselective addition of aryl iodides to norbomene has been reported using a palladium(II) complex of (5, iS )-CHIRAPHOS. The reaction of norbomadiene with 4-methoxyiodobenzene proceeded with 30% ee (eq 5). Enantioselectivities were dependent upon phosphine structure (see (+)-trans-(2S,3S)-Bis(diphenylphosphino)bicyclo[2.2.1 ]hept-5-ene). 

The chiral molecular receptor (35) has been used to effect enantioselective cyclization of the enone (36). The complex of (36) and (35) undergoes energy transfer from the ketonic acceptor to (36) and results in its conversion into the cyclobutanes (37) and (38) in a total yield of 21%. Bach et aV have continued their investigations of enantioselective additions mediated by the chiral lactam hosts (39). The present reactions involve intra and intermolecular additions of quinolone systems (40) at -60°C in toluene as solvent. The irradiation affords the cycloadducts (41) and (42). As can be seen, the ee of the products is high and the chemical yields are also good. An extension of the work to intermolecular reactions of the quinolone (43) was also reported. The additions of the alkenes... 

In the area of enantioselective synthesis see Enantio selectivit ), the development of catalytic carbon-carbon bond-forming reactions that proceed under mild conditions in an enantioselective fashion (ee > 95%) remains a challenging objective.Among a great variety of metallic complexes, Zr-containing chiral catalysts can promote efficient and highly enantioselective additions of nucleophilic fragments such as alkylmetals and cyanides to C=0 and C=N bonds. Moreover, Zr-based metallocenes promote additions of alkylmetals to carbon-carbon double bonds, reactions that do not easily occur with other catalysts. One another important feature is that the product of the asymmetric addition of an alkylmetal to an alkene produces a chiral alkylmetal that can be further functionalized. 

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