Rhodium-catalysed reactions allylation

Iodonium ylides (136), generated in situ with bisacetoxyiodobenzene, are converted to allyl- or benzyl-substituted oxonium or sulfonium ylides (137) via rhodium- or copper-catalysed carbene transfer.115 Such ylides undergo [1,2]- or [2,3]-rearrangement to the corresponding 2-substituted heterocycles (138). An example of the rhodium-catalysed reaction is reported in Scheme 36. 

The regio- and stereo-selective rhodium-catalysed allylic alkylations of chelated enolates have been investigated.25 It has been found that the Rh-catalysed allylic alkylation is as efficient and versatile as the Pd-catalysed version. In reactions of chelated enolates with suitable protecting groups, high yields and selectivities were obtained, and the regioselectivity can be directed by the reaction parameters. 

Access to a 1,4-dicarbonyl substrate has been realised in several ways. Examples include alkylation of imines with 2-alkoxy-allyl halides (equivalents of 2-halo-ketones),addition of /3-ketoester anions to nitroalkenes, followed by Nef reaction,and rhodium-catalysed carbonylation of 2-substituted acrolein acetals. The dialdehyde (as a mono-acetal) necessary for a synthesis of diethyl furan-3,4-dicarboxylate was obtained by two successive Claisen condensations between diethyl succinate and ethyl formate, as shown in the sequence below. 

Palladium is a useful catalyst in several reactions which lead to keto-esters. p-Keto-esters react with allylic carbonates, with catalysis by palladium, in a decarboxylative allylation reaction. y-Keto-esters are prepared, in reasonable yield, by the palladium-catalysed regioselective oxidation of Py-unsaturated esters. y-Keto-esters are obtained in good yield by the palladium-catalysed Reformatsky reaction of ethyl bromoacetate and acid chlorides. Derivatives of y-ketopimelic acid are formed by the rhodium-carbonyl-catalysed reaction of derivatives of acrylic acid with carbon monoxide. A mild method for the conversion of propiolic esters into P-keto-esters via thiol addition has been reported (Scheme 63) it has been used in a formal synthesis of ( )-thienamycin. 

Enantioselective synthesis of homopropargyl amines can be effected through copper-catalysed reaction of an allenyl boron reagent with aldimines. The first nucleophilic allylation of r-electrophiles by allylboron reagents has been achieved enantioselectively using a chiral rhodium catalyst (Scheme an allylrhodium intermediate has been implicated. Similar additions of R CH=CR BF3K have also been reported. ... 

The regio- and enantio-selective rhodium-catalysed 5isf2 reactions between substituted anilines and racemic tertiary allylic trichloroacetimidates give a,a-disubstituted allylic A -arylamines in moderate to high (51-92%) yields with S 2 S 2 ratios from 5 1 to >99 1 and 52 to 96% ee The catalyst was prepared from [RhCl(ethylene)2]2 and trans-2,5-(4-fluorophenyl)bicyclo [2,2,2] octadiene. 

Several years ago transition metal mediated reactions in the area of C-glycoside synthesis were primarily limited to palladium and to a lesser extent nickel and manganese. Over the last few years several other metals, including chromium, molybdenum, tungsten, cobalt, and rhodium, have been utilized in C-glycoside synthesis. This section discusses the chemistry of palladium, which is divided into Stille-type couplings and 7T-allyl complexes. This is followed by considerations of the chemistry of chromium and the above-listed metals. A review by Frappa and Sinou entitled Transition Metal Catalysed Fimctionalization at the Anomeric Center of Carbohydrates appeared in early 1997 [55]. 

Other organic processes facilitated by metal carbonyl clusters include a palladium carbonyl catalysed Diels-Alder reaction the selective reduction of aromatic nitro compounds using rhodium and ruthenium phosphine-carbonyls aza- and oxa-carbonylations of allyl phosphates by rhodium carbonyls Michael reactions of alkoxy-alkenones using iron... 

This reaction is catalysed by RhClajSHjO, in the presence of a trace of allyl alcohol. The mechanism is thought to include two insertion steps, and the intermediacy of a rhodium-hydride species. ... 

The carbonylation of nitrobenzene to phenyl isocyanate is catalysed by [RhCl(CO)2]2 + L (L=MoCl6 or py.H+Cl- >), [RhH(CO)(PPh3)3], = and PdCl2-pyMe+ Carbonylation of allylic substrates has also been studied in detail rhodium phosphine complexes [e.g., RhCl(PPh3)s] are particularly useful for the synthesis of AT-alkyl-2-pyrrolidones [reactions (6)], whereas the carbonylations of allylic alcohols to vinylacetate esters [reaction (7)] are best carried out with [PdCl2(PAr3)a]10MCl2 (M=Sn or Ge). ... 

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