Rhodium allyl halides

The simple procedure for the carbonylation of allyl halides has been extended in the high yielding solid-liquid two-phase conversion of allyl phosphates into amides (60-80%) under the influence of a rhodium carbonyl cluster in the presence of primary or secondary amines (Scheme 8.8). A secondary product of the reaction is the allylamine, the concentration of which increases as the pressure of the carbon monoxide is reduced, such that it is the sole product (ca. 80%) in the absence of carbon monoxide [28],... 

There are several relevant aspects of rhodium enolate chemistry. Rh(I) catalyzes the isomerization of allylic aUtoxides to enolates. We welcome this reaction done in a direct thermochemical context analogous to the related isomerizations of allyl halides , ethers and allyl amines . From the enthalpies of formation of allyl alcohol and propanal (—185.6 and —124.5 kJmol ), and their respective gas phase deprotonation enthalpies (1564 and 1530 kJ mol 252,253 jj. jjg concluded that the rearrangement of the allyloxide to propen-1-olate is exothermic by 95 kJmoR. ... 

Carbonylation of allylamines can produce pyrrolidones, although relatively high pressures of CO are usually required. Homogeneous rhodium catalysts are preferred and, using similar catalysts, the pyrrolidones can be obtained from allylic halides, CO and ammonia (Scheme 28). ... 

Hydrogenation of C=C, C=NOH, C=N. Ham and Coker found rhodium-alumina the catalyst of choice for hydrogenation of vinylic and allylic halides with minimal hydrogenolysis, for example ... 

Allyldiethylamine behaves similarly, but the yields are low since neither the starting amine nor the products are stable to the reaction conditions. For the efficiency of the cyclopropanation of the allylic systems under discussion, a comparison can be made between the triplet-sensitized photochemical reaction and the process carried out in the presence of copper or rhodium catalysts whereas with allyl halides and allyl ethers, the transition metal catalyzed reaction often produces higher yields (especially if tetraacetatodirhodium is used), the photochemical variant is the method of choice for allyl sulfides. The catalysts react with allyl sulfides (and with allyl selenides and allylamines, for that matter) exclusively via the ylide pathway (see Section 1.2.1.2.4.2.6.3.3. and Houben-Weyl, Vol. E19b, pll30). It should also be noted that the purely thermal decomposition of dimethyl diazomalonate in allyl sulfides produces no cyclopropane, but only the ylide-derived product in high yield.Very few cyclopropanes have been synthesized by photolysis of other diazocarbonyl compounds than a-diazo esters and a-diazo ketones, although this should not be impossible in several cases (e.g. a-diazo aldehydes, a-diazocarboxamides). Irradiation of a-diazo-a-(4-nitrophenyl)acetic acid in a mixture of 2-methylbut-2-ene and methanol gave mainly l-(4-nitrophenyl)-2,2,3-trimethylcyclo-propane-1-carboxylic acid (19, 71%) in addition to some O-H insertion product (10%). ... 

The importance of the nucleophilicity of the heteroatom for product partitioning is shown for the interaction of ethyl diazoacetate with allyl halides, e.g. formation of 29 and 30. In contrast to the result for this diazo compound, rhodium-catalyzed reaction of diethyl di-azomalonate with allyl bromide yields practically no cyclopropane [Rh2(OAc)4 diethyl al-lyl(bromo)malonate (86%) and diethyl 2-bromomethylcyclopropane-l,l-dicarboxylate (6%) RhjCCO) 72 and 10%].2 ... 

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. 

An attractive pathway with a lot of potential uses the transition metal mediated reaction of organic halides with carbon monoxide. Suitable substrates are organic halides capable of oxidative addition to low-valent transition metal compounds. Insertion of carbon monoxide and reductive elimination of an acid halide will complete the catalytic cycle. In tins way it was shown tiiat allyl chloride yields butenoic acid chloride in >80% yield accor g to equation 22)P As well as palladium, rhodium and iridium also act catalytically. It is of no surprise that allylic halides, benzylic halides and aryl halides in particular are readily converted to acid halides. Simple aliphatic halid undergo the oxidative addition step more slowly and, if they cany hydrogen atoms on an sf hybridized C atom in the -position to the halogen atom, may give alkenes via 3-hydrogen elimination. Alkenes can also be converted to acid halides widi carbon monoxide in the presence of transition metal catalysts in solvents such as methylene chloride or tetrachloromethane. ... 

Suitable catalysts for ring closure reactions are cobalt carbonyls [123, 280, 673, 674], rhodium carbonyls [280, 678], iron carbonyl [123] and certain palladium compounds [679]. Nickel carbonyls, the active catalysts in the Reppe syntheses, are inactive in most cases [123, 673]. A few examples in which nickel is active are the formation of phenols from allyl halides, acetylene and carbon monoxide, which is only a side reaction, and the mechanistically unclear formation of lactones from allyl carbinol and bu-tyne-l-ol-4 [438]. 

Rhodium.—The formation of rhodium(i) complexes with allenes has been much studied for rhodium(i)-halide compounds. Allenes also react with the diketone complexes Rh(LL)(C2H4)a where LL = acetylacetonato or dibenzoylmethanato, to form rhodium(i)-allene compounds. In this case an A"-ray crystal structure determination has shown that the product contains the allene tetramer (19) bonded to the rhodium by two w-allyl bonds. ... 

Rhodium.— The kinetics of reaction of Rh(A -C6H5)(CO)(PR3) with alkyl and with benzyl halides indicate a second-order rate law and nucleophilic attack by the rhodium at the a-carbon of the alkyl or benzyl halide. The kinetics of reaction of the above rhodium complex with PR3 = PPhs with allyl halides suggest a more complicated mechanism. ... 

Recently, hydrosilanes are also employed for the silylation of aryl halides in the presence of a palladium,platinum, or rhodium catalyst. In view of atom efficiency, this procedure has an advantage. Palladium-catalyzed reactions are suitable for the silylation of electron-rich aryl halides, whereas rhodium-catalysis works well with a wide range of aryl halides (Scheme 3-17). Silylation of allyl halides with trichlorosilane proceeds in the presence of a copper catalyst. ... 

Evans and Uraguchi also examined the rhodium-catalyzed allylic alkylation with hard nucleophiles [31]. Aryl organozinc halides proved optimal nucleophiles for the regio- and stereospecific allylic alkylation of enantiomerically enriched unsymmetrical allylic alcohol derivatives (Tab. 10.4). The reaction occurs with net inversion of absolute... 

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. 

Allylic amide isomerization, 117 Allylic amine isomerization ab initio calculations, 110 catalytic cycle, 104 cobalt-catalyzed, 98 double-bond migration, 104 isotope-labeling experiments, 103 kinetics, 103 mechanism, 103 model system, 110 NMR study, 104 rhodium-catalyzed, 9, 98 Allylnickel halides, 170 Allylpalladium intermediates, 193 Allylsilane protodesilylation, 305 Aluminum, chiral catalysts, 216, 234, 310 Amide dimers, NMR spectra, 282, 284 Amines ... 

Rhodium and palladium allyl complexes form from the reaction of a Tl(III)allyl compound with a metal halide ... 

Enolates can also be prepared by rhodinm-catalyzed isomerization of allylic Uthinm alcoholates, such as 14 (equation 5)". Subsequent treatment of the intermediately formed rhodium hydride complexes (15 and 16) with an electrophile led to the formation of various products. For example, alkyl halides gave a-alkylated ketones (17) in good yields, as shown in Table 4. Interestingly, addition of benzaldehyde under kinetically controlled... 

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