Lactones transfer catalysts

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Carboxylic acids can be converted into the corresponding peroxy acids using peroxydisulfate in the presence of a phase transfer catalyst in good to excellent yields . When o-methylbenzoic acid was treated with sodium peroxydisulfate in the presence of Ag(I)/Cu(It), the corresponding lactone was obtained in 56% yield. Acyl radicals were also trapped by quinohnes or alkenes in the presence of peroxydisulfate to give the products in high yields. 

The thioxo group of (265 X = S) (see Section 8.25.3.6.5) was alkylated with Mel in ethanol <76M183>. 5 -Methylation on a phase-transfer catalyst, however, resulted in the cleavage of the lactone ring <82S1073>. 

Asymmetric nitro-Michael reactions of methyl vinyl ketone (MVK) in the presence of bicyclic guanidine with a benzhydryl group led, disappointedly, to low asymmetric induction (9-12%) [21a] Trials for the reaction of 0 ,p-unsaturated y- or 8-lactones with pyrrolidine in the presence of the conjugate acids of a bicyclic guanidine [50] or the Murphy s guanidine [24a] (R = Me in Scheme 4.7) resulted in the production of racemic compounds. The latter phase transfer catalyst (PTC) catalyses the nitro-Michael addition of chalcone but with limited range (70% yield, 23% ee) [24c]. 

Cyclization of the methanesulfonate of 12-hydioxydodecanoic acid in toluene with aqueous sodium bicarbonate and a 1% cross-linked, DF 0.04, (polystyrylmethyl)tri-n-butylphosphonium ion phase transfer catalyst gave 66% yield (1321. However, the concentration of substrate in the final reaction mixture was 2.3 mM, no higher than in most high dilution experiments. A more promising method is solid-liquid phase transfer catalysis. A 0.1M suspension of the potassium salt of 12-bromododecanoic acid in toluene containing 2.5 Mm tetra-n-butylammonium bromide was heated at 90 °C to give 95% of the 13-membered lactone (Equation 32) (1331. Effective concen-... 

In 1998, Peterson and Larock showed that Pd(OAc)2 in combination with NaHCOs as a base in DMSO as solvent catalyzed the aerobic oxidation of primary and secondary allylic and benzylic alcohols to the corresponding aldehydes and ketones, respectively, in fairly good yields [70]. In both cases, ethylene carbonate and DMSO acted both as the solvent and as the ligand necessary for a smooth reoxidation [71]. Similarly, PdCl2, in combination with sodium carbonate and a tetraalkylammonium salt, Adogen 464, as a phase transfer catalyst, catalyzed the aerobic oxidation of alcohols for example, 1,4- and 1,5-diols afforded the corresponding lactones (Eq. (5.11)) [72, 73]. 

The remarkable efficiency of Shiina lactonization, which was mediated by acyl-transfer catalysts with MNBA, has been already demonstrated in a variety of successful total syntheses of natural products and biologically active compounds by other researchers (totaling over 370 citations to date). Furthermore, over 900 successful reactions using MNBA have been reported for the preparation of a variety of substrates including ester, amide, and lactone moieties. 

The intermediate N-acylpyridinium salt is highly stabilized by the electron donating ability of the dimethylamino group. The increased stability of the N-acylpyridinium ion has been postulated to lead to increased separation of the ion pair resulting in an easier attack by the nucleophile with general base catalysis provided by the loosely bound carboxylate anion. Dialkylamino-pyridines have been shown to be excellent catalysts for acylation (of amines, alcohols, phenols, enolates), tritylation, silylation, lactonization, phosphonylation, and carbomylation and as transfer agents of cyano, arylsulfonyl, and arylsulfinyl groups (lj-3 ). 

For unsaturated lactones containing an endocyclic double bond also the two previously described mechanisms are presumably involved and the regio-selectivity of the cyclocarbonylation is governed by the presence of bulky substituents on the substrate. Inoue and his group have observed that the catalyst precursor needs to be the cationic complex [Pd(PhCN)2(dppb)]+ and not a neutral Pd(0) or Pd(II) complex [ 148,149]. It is suggested that the mechanism involves a cationic palladium-hydride that coordinates to the triple bond then a hydride transfer occurs through a czs-addition. Alper et al. have shown that addition of dihydrogen to the palladium(O) precursor Pd2(dba)3/dppb affords an active system, in our opinion a palladium-hydride species, that coordinates the alkyne [150]. 

The reactions of aldehydes at 313 K [69] or 323 K [70] in CoAlPO-5 in the presence of oxygen results in formation of an oxidant capable of converting olefins to epoxides and ketones to lactones (Fig. 23). This reaction is a zeolite-catalyzed variant of metal [71-73] and non-metal-catalyzed oxidations [73,74], which utilize a sacrificial aldehyde. Jarboe and Beak [75] have suggested that these reactions proceed via the intermediacy of an acyl radical that is converted either to an acyl peroxy radical or peroxy acid which acts as the oxygen-transfer agent. Although the detailed intrazeolite mechanism has not been elucidated a similar type IIaRH reaction is likely to be operative in the interior of the redox catalysts. The catalytically active sites have been demonstrated to be framework-substituted Co° or Mn ions [70]. In addition, a sufficient pore size to allow access to these centers by the aldehyde is required for oxidation [70]. 

Upon fonnation of intermediate LI, conjugate addition to a chalcone and subsequent proton transfer is proposed to lead to enolate LIII (Scheme 37). An intramolecular aldol addition provides activated carboxylate LIV in which alkoxide acylation regenerates the catalyst and delivers p-lactone LVI which, upon decarboxylation, gives rise to a trisubstituted cyclopentene. 

ROP of p-lactones is highly prone to numerous side reactions, such as transester-fication, chain-transfer or multiple hydrogen transfer reactions (proton or hydride). Specifically, the latter often causes unwanted functionalities such as crotonate and results in loss over molecular weight control. Above all, backbiting decreases chain length, yielding macrocyclic structures. All these undesired influences are dependent on the reaction conditions such as applied initiator or catalyst, temperature, solvent, or concentration. The easiest way to suppress these side reactions is the coordination of the reactive group to a Lewis acid in conjunction with mild conditions [71]. p-BL can be polymerized cationically and enzymatically but, due to the mentioned facts, the coordinative insertion mechanism is the most favorable. Whereas cationic and enzymatic mechanisms share common mechanistic characteristics, the latter method offers not only the possibility to influence... 

In the asymmetric hydrogenation of the (R)-phenylglycine derivative (54) in the presence of an achiral catalyst the stereoselectivity was reported 89) to be low. The lactone (55) could subsequently be converted into (S)-aspartic acid 89). This reaction sequence is an example of the intramolecular transfer of chirality with subsequent disappearance of the original chiral center. 

Oxidative degradation of the catalyst (e.g. lactone formation by Baeyer-Villiger oxidation) competes with oxygen transfer and is the reason a relatively high catalyst loading is required. In their search for more robust, yet (comparatively) readily available ketone catalysts, Shi et al. prepared the carbamates 12a-c [20-22], Use... 

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