Cinnamyl carbonate

Allylic alkylations of cinnamyl carbonate by sodium malonate have been studied with a series of ruthenium catalysts, obtained from the azohum salts 126-128 and the ruthenium complex 129 (Scheme 2.25) in MeCN or THF to give moderate yields of mixtures of alkylated products in the allylic and ipi o-carbons (90 10 to 65 35). The observed regioselectivity is inferior to similar ruthenium systems with non-NHC co-ligands. The stereoelectronic factors which govern the observed regioselectivity were not apparent [102]. 

Scheme 2.25 Generation of ruthenium catalysts for the allyhc alkylation of cinnamyl carbonate...

Pd(0)-catalyzed allylations of 4(5)-nitroimidazole, 2-methyl-4(5)-nitroimidazole, 4(5)-bromoimidazole and 4(5)-methoxyimidazole resulted in complicated mixtures, which did not necessarily reflect the tautomeric ratios of the starting material [7], For example, poor regioselectivity for the products (70 and 71) was observed in the Tsuji-Trost reaction of 4(5)-bromoimidazole with cinnamyl carbonate. However, the same reaction with 4(5)-nitroimidazole and 2-methyl-4(5)-nitroimidazole led predominantly to the l-allylation products. In addition, removal of the 77-imidazole allyl groups can be selectively effected under mild conditions by Pd-catalyzed ic-allyl chemistry [55],... 

The phosphoramidite ligands that are the focus of the remainder of this chapter have prompted the investigation of ligands containing related structures. Iridium complexes of aspartic acid-derived P-chirogenic diaminophosphine oxides (DlAPHOXs) catalyze the amination [62] and alkylation [63] of aUyhc carbonates (Scheme 6). With BSA as base and catalytic amounts of NaPFs as additive, branched amination and alkylation products were obtained from cinnamyl carbonates in excellent yields and enantioselectivities. However, the yields and enantios-electivities were lower for the reactions of alkyl-substituted aUyhc carbonates. Added LiOAc increased the enantioselectivities of aUyhc alkylation products. 

The scope of allylic electrophiles that react with amines was shown to encompass electron-neutral and electron-rich ciimamyl methyl carbonates, as well as furan-2-yl and alkyl-substituted allylic methyl carbonates. An ort/io-substituted cinnamyl carbonate was found to react with lower enantioselectivity, a trend that has been observed in later studies of reactions with other nucleophiles. The electron-poor p-nitrocinnamyl carbonate also reacted, but with reduced enantioselectivity. Allylic amination of dienyl carbonates also occur in some cases with high selectivity for formation of the product with the amino group at the y-position over the s-position of the pentadienyl unit [66]. Arylamines did not react with allylic carbonates under these conditions. However, they have been shown to react in the presence of the metalacyclic iridium-phosphoramidite catalysts that are discussed in Sect. 4. 

Markovic and Hartwig isolated and characterized the first intermediate in iridium-catalyzed allylic substitution [100]. They isolated the metalacyclic iridium-phosphor-amidite fragment containing COD and the olefinic portion ofN- l -phenylallyl)aniline, the product of the allylic substitution reaction between cinnamyl carbonate and aniline (5 in Scheme 22). This complex containing the product of allylic substitution was first detected by NMR spectroscopy during catalytic reactions. It was then isolated, prepared independently, and shown to be chemically and kinetically competent to be an intermediate in allylic substitutions. 

In addition to isolating complex 5, Markovic and Hartwig performed kinetic studies on the amination of methyl cinnamyl carbonate with aniline. The proposed mechanism involves reversible dissociation of product, reversible, endothermic oxidative addition of the allylic carbonate to form a 7i-allyliridium species, and irreversible nucleophilic attack on the 7i-allyliridium intermediate, as depicted in... 

Scheme 22 Catalytic cycle for the reaction of aniline with methyl cinnamyl carbonate catalyzed by a metalacyclic iridium-phosphoramidite complex...

Sulfonamides are suitable pronucleophiles, as was first established with N-tosyl-amines [59]. Particularly good results were achieved with L2 as ligand and activa-hon of the catalyst with TBD (Scheme 9.26) for example, the regioselectivity of b/l = 98 2 and an ee-value of98% were obtained in the reaction of LiN(CH2Ph)p-Ts with cinnamyl carbonate. With a substrate containing a sphsubstituent, however,... 

In an exploratory study, Cu-alkoxides were found to be superior to Zn-alkoxides, and tert-butyl cinnamyl carbonate superior to methyl cinnamyl carbonate, which underwent transesterificahon. Both, arylallyl and alkylallyl carbonates were successful as substrates. 

As shown in equation 29, l,l-bis(iodozincio)ethane was reacted with cinnamyl carbonates in the presence of Pd(0) catalyst with chiral phosphine ligand, MOP51,52. The formed organozinc intermediate was treated with propargyl bromide under the mediation of copper salt. The observed asymmetric induction reached up to 33% . 

Allylic substitution Pd dendrimer (Ph2PCH2)2N cinnamyl carbonate 95 (Pd) 262 n.a. Brinkmann, 1996... 

Recently, a new ruthenium catalyst that also provides regioselective allylic alkylation has been reported. In DMF, a highly branched alkylation product of cinnamyl carbonate vsdth malonate anion was obtained in quantitative yield (branched/line-ar = 14/1) within 30 min in the presence of 1 mol% of [(C5Me5)Ru(MeCN)3]PF6 catalyst (Eq. 5.30) [46]. 

A cinnamyl carbonate is cleaved electrochemically ( -2.3 V, Hg, CH3CN) in preference to the cinnamyl carbamate. ... 

The catalytic activity, selectivity, and catalyst stability is improved for Trost-Tsuji G-G coupling of cinnamyl carbonate and ethyl acetoacetate with a water-soluble Pd/TPPTS catalyst (sodium salt) when performed in [G4GiIm]Gl. " These Pd-catalyzed allylation reactions can also be performed under microwave conditions employing mixtures of [G2GiIm]BF4/water. ... 

Several recent studies have revealed the dichotomous relationship between the regioselectivity of reactions of unsymmetrical allyl complexes of palladium and that of reactions of unsjmmetrical allyl complexes of other metals. An isolated molybdenum-allyl complex containing an allyl group derived from methyl cinnamyl carbonate (PhCH=CHCH2C)COjMe) reacts with the sodium salt of dimethyl malonate in the presence of a source of CO to generate the branched substitution product (Equation 11.41). The addition of nucleophile to this allyl complex has been shown to occur by retention of configuration, perhaps by initial attack at the metal, rather than the more common external attack at Are allyl group. ... 

Comparison of the results of Tsuji-Trost coupling of ethyl cinnamyl carbonate and ethyl acetoacetate (Scheme 60) in biphasic mixtures either with water or with an ionic liquid showed clear advantage of using the IL solvent (292). The organic reactants are much better soluble in [bmim]Cl than in water which leads to faster reactions and in the absence of water formation of cinnamyl alcohol as by-product is avoided. 

The Pd(0)-catalyzed reaction of ethyl cinnamyl carbonate with /S-naphthol has been shown to give first the O-aUylated kinetic product 36 (Scheme 19), which is rearranged... 

Studies reporting substituent effects on the palladium- and copper-catalysed Sonogashira coupling reaction between an aryl iodide and an alkyne the 5 2 allylic substitution reactions between benzyl amine and racemic allyl carbonates substituted with a j -X-Ph- group on C(l) in the presence of a Rh(15,15, 2/ ,2/ -tangphos)(COD)Bp4 catalyst the stereoselective 5 2 reactions between a-substituted linear 0-ketoesters and meta- and /Jura-substituted cinnamyl carbonates generating vicinal quaternary and tertiary stereocenters in the presence of an Ir-V-arylphosphoramidite catalyst, TBD, and LiOBu-t identity vinyl halide reactions the S N... 

In order to complement earlier studies showing that IV-alkyl-substituted ben-zimidazolylidene-ruthenium complexes were efficient catalysts for the regiose-lective alkylation of cinnamyl carbonate by dimethyl malonate or 1,3-diketones, as well as etherification of allylic halides by phenols, Bruneau and co-workers prepared a wide range of imidazolinium 38, tetrahydropyrimidinium 39, and benzimidazolium salts 40 that were screened as NHC ligand precursors in various allylic substitution reactions (Equation (7.9)). Unfortunately, linear versus branched selectivities were only modest, and no characterisation of the [(NHC)Ru(Cp )] complexes assumed to take part in the reaction could be achieved, thereby preventing any further rational ligand modification that would have helped refine the catalytic system. 

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