Amidation rhodium-catalysed

To date most of the nitriles studied have been simple alkyl or aromatic derivatives with little other functionality. We recently attempted to extend the reaction to iV-protected a-aminonitriles, derived by dehydration of a-aminoacid amides (Path A, Scheme 25), but this proved unsatisfactory, and therefore we investigated an alternative diazocarbonyl based route in which the order of steps was reversed, i.e. a rhodium catalysed N-H insertion reaction on the amide followed by cyclodehydration to the oxazole (Path B, Scheme 25). 

The application of the Moody s procedure to the solid-phase synthesis involved as key step the rhodium-catalysed decomposition of resin-bound a-diazo-P-ketoesters 146 in the presence of primary amides to afford N-H insertion products 147 cyclodehydration gave 148, further elaborated during cleavage from the resin towards substituted oxazoles 149 <01OL2173>. 

Rhodium complexes, formed in situ with [Rh(COD)2]BF4 and monodentate chiral spiro phosphite and phosphine ligands, catalyse the AH of both (Z)- and (E)-P-arylenamides with up to 97% ee. A library of 19 chiral binol-monophosphite ligands containing a phthalic acid secondary bis-amide group has been synthesized and screened for use in stereocontrol of rhodium-catalysed hydrogenation of several prochiral dehydroamino esters and enamides. Spectroscopic and computational studies... 

An ab initio method has been employed to study the mechanism of the thermal isomerization of buta-1,2-diene to buta-1,3-diene. The results of the study have indicated619 that the transformation proceeds in a stepwise manner via a radical intermediate. Experimental free energies of activation for the bond shift in halocyclooctatetraenes have been reported and analyzed by using ab initio MO calculations.620 The isomerization of hexene using a dihydridorhodium complex in dimethyl sulfoxide has been reported,621 and it has been suggested622 that the Pd(II)-catalysed homogeneous isomerization of hexenes proceeds by way of zr-allylic intermediates. A study has been made623 of alkene isomerization catalysed by the rhodium /-phosphine-tin dichloride dimeric complex, and the double-bond isomerization of olefinic amines over potassium amide loaded on alumina has been described.624... 

The first successful catalytic animation of an olefin by transition-metal-catalysed N—H activation was reported for an Ir(I) catalyst and the substrates aniline and norbornene 365498. The reaction involves initial N—FI oxidative addition and olefin insertion 365 - 366, followed by C—FI reductive elimination, yielding the animation product 367. Labelling studies indicated an overall. vyw-addition of N—FI across the exo-face of the norbornene double bond498. In a related study, the animation of non-activated olefins was catalysed by lithium amides and rhodium complexes499. The results suggest different mechanisms, probably with /5-arninoethyl-metal species as intermediates. 

The Rh(II)-catalysed intramolecular C-H insertion of diazoacetamide in water has been studied.49 This study assessed the factors governing the preferential intramolecular C-H insertion versus O-H insertion with the solvent. The hydrophobic/hydrophilic nature of the amide substituent appeared to be the most significant contribution driving the reaction towards C-H insertion. The nature of the rhodium catalyst precursor also modifies the reaction outcome [Rh2(OAc)4 enhancing the O-H insertion],... 

A highly enantioselective 1,4-addition of aryltrialkoxysilanes ArSi(OR)3 to a,fi-unsaturated esters and amides RCH=COX (X = OR, NR R") was catalysed by a chiral rhodium complex generated from [(MeCN)2Rh(COD)]BF4 and (S)-BINAP in aqueous dioxane.243... 

One of the most famous examples is a general synthesis of aromatic amino acids 14, both natural like phenylalanine 14 Ar = Ph, and unnatural. The easily prepared /V-acyl enamines 12 are hydrogenated in methanol catalysed by the rhodium-DIPAMP complex, to give the saturated amides 13 in almost perfect ee. Hydrolysis releases the amino acid 14. This process was discovered by Knowles at Monsanto. 

A convenient route to polysubstituted oxazoles was developed through a variation on the Robinson-Gabriel synthesis in which the key 1,4-dicarbonyl compounds were obtained by a rhodium carbene N-H insertion reaction. Dirhodium tetraacetate catalysed reaction of primary amides 103 and diazocarbonyl compounds 107 gave a-acylaminoketones 108, which were converted into 109 by cyclodehydration using the Wipf and Miller protocol <04T3967>. 

Reactions with aikynes may aiso result in the formation of cyclized products. Thus a ruthenium-catalysed reaction with aromatic amides has been used to give isoquinoline derivatives. On the basis of values of the kinetic isotope effect, A h/ d> proposed that the rate-determining step is a concerted acetate-assisted metalation-deprotonation process to yield the intermediate (30), followed by aikyne insertion and ring closure. The reaction of arylketones with alkynes may yield indenols when catalysed by rhodium cyclopentadienyl in the presence of silver and copper salts. The reaction proceeds regioselectively, so that reaction of acetophenone with 1-phenyl-1-propene... 

Aldehydes react with the lithio-derivatives of a-diazo-esters to give /3-hydr-oxy>a-diazo-esters, which in turn undergo rhodium(ii)-catalysed decomposition to give /3-keto-esters./3-Keto-amides are obtained in moderate to high yield from the acylation of amide enolates with mixed anhydrides. In a general reaction, orthoformates react with acidic methines to give /3-keto-aldehydes, isolated as their dialkyl acetals [equation (16)]. ... 

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