Diastereoselective rhodium-catalyzed addition

Similarly, imines react with phenyltrimethyllead 101 in the presence of a rhodium catalyst, in water and air under ultrasonic irradiation at 35°C, to give the corresponding diarylmethylamines in good yields (Equation (114)). A moderate diastereoselectivity was observed when the rhodium catalyzed addition of (ort o-chlorophenylltrimethyl-lead 105 was done on a chiral />-tolucnesu I liny limine 104 (Equation (115)).127... 

Evans and co-workers simultaneously developed of the rhodium-catalyzed [4-+2 + 2] car-bocychzation reaction through the identification of a novel mode of reactivity for the five-membered metallacycle intermediate [14, 37]. Evans proposed that 1,3 dienes should be amenable to addition to this intermediate, which would provide a new reaction pathway. The tethered enyne 80 (Scheme 12.9), was expected to afford the metallacycle I, which, upon sequential incorporation of a butadiene and reductive ehmination, would afford the desired 5,8-fused product 81. Additionally it was rationahzed that this transformation should be highly diastereoselective, as outlined in Scheme 12.10. Treatment of the heteroatom-tethered enyne I under standard carbocyclization (Pauson-... 

When the rhodium-catalyzed reaction of aryllead reagents in water and under an atmosphere of air was applied to a chiral glyoxylate hydrate, it gave the corresponding addition products in high yields (Equation (116)). The diastereoselectivity of the reactions were remarkably improved by using water as the solvent.128... 

Imines derived from N tert butanesulfinamide also undergo diastereoselective rhodium(I) catalyzed addition of arylboronic acids [61] (Scheme 1.16), a reaction that has been primarily developed for catalytic asymmetric processes (see below). 

Electrophilic aldehydes have been also generated through a rhodium catalyzed hydroformylation process of alkenes, which has been combined with the aldol addition catalyzed by prohne (1,30 mol%) in a tandem reaction sequence, providing the aldol products 4 in good yields (59-86%) and enantioselectivities (71-83%), but with low diastereoselectivities [20]. 

A diastereoselective approach to these chiral building blocks was developed by Ellman (Scheme 8.15) [40]. Thus, N-tert-butylsulfinyl aldimines 57 were employed as electrophiles in the rhodium/phosphine 58-catalyzed addition of arylboronic acids. Whereas Ellman s procedure requires heating, Batey discovered that an amine base allows the reaction to take place at ambient temperature [41]. However, it is worth noting that Ellman s process can also be carried out in an enantioselec-tive way by using N-diphenylphosphinoyl aldimines 48 as substrate and Degu-PHOS (56) as ligand (87-97% yield, 88-94% ee) (Scheme 8.14 Figure 8.4). 

Maddaford and co-workers have reported the diastereoselective synthesis of C-gly-coside 34m by use of rhodium-catalyzed conjugate addition [27] (Scheme 4.13). The reaction is efficiently catalyzed by cationic rhodium catalysts such as [Rh(cod)2]BF4,... 

The rhodium-catalyzed one-pot enolboration/hydroformylation/aldol addition sequence was applied for the regioselective and diastereoselective formation of carbocydic quaternary centers from acydic olefins (Equation 7.13) [135]. 

Scheme 2.41 Enantioselective rhodium-catalyzed conjugate addition of a borane and subsequent diastereoselective aldol addition of boron enolate 140.

Scheme 5.112 Rhodium-catalyzed enantioselective conjugate addition and subsequent diastereoselective aldol addition/allylation of boron enolate 438. Model for rationalizing the stereochemical outcome.

Rhodium complexes catalyze 1,2-addition of main group metal compounds to aldimines as well. Table 5 summarizes the reported methods. Electron-withdrawing substituents such as sulfonyl and acyl groups on the imino nitrogen atom are important to obtain sufficiently high reactivity. Asymmetric synthesis (diastereoselective and enantioselective) has also been accomplished. 

Maddaford reported the diastereoselective synthesis of C-glycosides 29 using conjugate addition catalyzed by cationic rhodium catalysts such as [Rh(COD)2]BF4 (Eq. 1) [24]. Addition of phosphine hgands to the reaction system inhibited the conjugate addition. It is likely that the enone 28 derived from the pyranose is less reactive toward the conjugate addition. 

Rhodium( I)-catalyzed hydroformylation of cyclic enol acetals 1 leads to acetal-protected syn-3,5-dihydroxyalkanals 2 with extraordinarily high levels (>50 1) of diastereoselectivity (Scheme 5.2) [2]. The diastereoselectivity cannot be ascribed to any obvious steric bias, and serves as a powerful demonstration that the hydroformylation reaction may be subject to exquisite stereoelectronic control. Indeed, while the addition of a pseudo-axial methyl group to the acetal carbon (as in acetonide 3) has a deleterious effect on the rate of the reaction, the sy -diastereomer 4 is still produced selectively, in what is surely a contra-steric hydroformylation reaction. 

In addition to copper and rhodium catalysts commonly used in the generation of metal carbene complexes, other transition metals have also been explored in the diazo decomposition and subsequent ylide generation.Che and co-workers have recently studied ruthenium porphyrin-catalyzed diazo decomposition and demonstrated a three-component coupling reaction of a-diazo ester with a series of iV-benzylidene imines and alkenes to form functionalized pyrrolidines in excellent diastereoselectivities (Scheme 20). ... 

Scheme 1.16 Rhodium(l) catalyzed arylboronic acid diastereoselective addition.

The addition of ethenylcarbene (Z)- or (i )-olefins proceeds with retention of configuration2. The simple diastereoselectivity of the rhodium(Il) acetate catalyzed reaction of 3-diazopropene with ethyl vinyl ether is good and affords cis-1 -ethoxy-2-vinylcyclopropane (3) as the major diastereomer (for procedure see Vol. El9b, p687)3,... 

Preparation of an useful synthon, the cyclic carbamate of L-daunosaminal (104), was achieved by sequential catalytic transformations of a key intermediate. Suitably protected propargyl diol 101, which was obtained by diastereoselective addition of allenyl stannate 99 to 0-benzyl (S)-lactyl aldehyde 100, was transformed as depicted in Scheme 18. Cycloisomerization to 3-deoxyglycal 103 was achieved by irradiation in the presence of tungsten hexacarbonyl, and subsequent nitrene insertion was catalyzed by rhodium acetate. Overall yield of the bicyclic daunosaminal (104) derivative from lactic acid derivative amounted to 44% [78]. 

Feringa recently reported a highly enantio- and diastereoselective one-pot conjugate arylation/allylation sequence (Scheme 8.42) [120] where the initial rhodium/ phosphoramidite-catalyzed conjugate addition of arylboronic acids in dioxane/ water was complemented by a Barbier-type indium-mediated allylation. 

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