Epoxides and Methanol

Previously, our group have reported cycloaddition of PO and CO2 to form PC promotes by a phosphonium salt covalently bound to PEG6000 with excellent yield and selectivities [14]. Further studies show that inorganic base/phosphonium 

120 °C c PO (10 mmol), BrTBDPEG150TBDBr (0.5 mmol), C02 (3 MPa), 120 °C, 1749 cm 1 corresponds to peak for carbonyl group of carbamic acid formed between C02 and BrTBDPEG150TBDBr. 1790 cm-1 was the carbonyl group absorption of the product PC. Reproduced from Ref. [15] by permission of The Royal Society of Chemistry 

Notably, an almost quantitative yield of DMC and 1, 2-diols can be attained under the optimized reaction conditions. Additionally, the catalyst is easily reused in almost consistent in yield and selectivity. This process eliminates the requirement for toxic and wasteful feedstocks such as phosgene and carbon monoxide and has successfully been applied to synthesize the other symmetric dialkyl carbonates and 1, 2-diols. 

Entry Molar ratio (EC MeOH) T/h EC conv. (%)b DMC yield (%)b 

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Optically pure tri(hydroxyalkyl)amines 29 (R = Me, t-Bu, cyclohexyl or Ph) have been obtained from enantiomerically pure epoxides and methanolic ammonia63. Tetraphenylsti-bonium trifluoromethanesulphonate, SbPhzj1 C.f 3S03, catalyses the reaction of epoxides with amines, e.g. diethylamine or aniline, to yield 2-hydroxyalkylamines in quantitative yields (equation 25)64. 

Bhanage BM, S-i Fujita, Ikushima Y et al (2003) Synthesis of dimethyl carbonate and glycols from carbon dioxide, epoxides and methanol using heterogeneous Mg containing smectite catalysts effect of reaction variables on activity and selectivity performance. Green Chem 5(1) 71—75... 

We ll start with the acid-catalysed reaction, because it is more similar to the examples we have just been discussing—opening happens at the more substituted end. Protonation by acid produces a positively charged intermediate that bears some resemblance to the corresponding bromonium ion. The two alkyl groups make possible a build-up of charge on the carbon at the tertiary end of the proto-nated epoxide, and methanol attacks here, just as it does in the bromonium ion. 

Bhanage, B. M. Fujita, S. Ikushima, Y Aral, M Synthesis of Dimethyl Carbonate and Glycols from Carbon Dioxide, Epoxides, and Methanol using Heterogeneous Basic Metal Oxide Catalysts with High Activity and Selectivity. Appl. Catal. A Gen. 2001,219,259-266. 

In this oxidative degradation, MTO decomposes into catalytically inert perrhenate and methanol. The decomposition reaction is accelerated at higher pH, presumably through the reaction between the more potent nucleophile H02- and MTO. The decomposition of MTO under basic conditions is rather problematic, since the selectivity for epoxide formation certainly profits from the use of nonacidic conditions. 

Jacobsen (1999) has carried out carbomethoxylation of asymmetric epoxides. Thus, the carbomethoxylation of (R)-propylene oxide with CO and methanol yields 92% of (3R)-hydroxybutanoic acid in greater than 99% ee. Similarly, the reaction of (/ )-epichlorohydrin gives 96% of 4-chloro-(3R)-hydroxybutanoic acid in greater than 99% ee. The catalyst consists of dicobalt octacarbonyl and 3-hydroxy pyridine. A continuous process for making enantiomeric 1-chloro-2-propanol has been suggested. With a suitable catalyst propylene reacts with O2, water, cupric and lithium chloride to give 78% of (S)-l-chloro-2-propanol in 94% ee. 

Several modifications of incubation conditions have neither stabilized the system nor enhanced activity. Acetone and methanol have been used as substrate carriers without affecting activity. Similarly, addition of NADH to the incubation media did not effect epoxidation. The enzymatic nature of the system has been confirmed by use of heat treated homogenates (100 C, 1 min). Incubation temperatures of 8, 20, and 30 resulted in progressively greater epoxidation rates and provided no evidence of heat lability. Thus, at this time it is not possible to identify a superior enzyme source for comparative studies in spite of the fact that in vivo measurements indicate oxidative metabolic activity in living mussels. 

To arrive at racemic coriolin, Danishef sky and coworkers chose to add an acetonyl fragment to a bicyclic enedione by Diels-Alder chemistry (Scheme LXXIII) Treatment of the resulting adduct 695 sequentially with a series of conventional reagents produced the key intermediate 696. Suitable aldolization deUvered 697, the functionality in which was adjusted by deconjugation and reduction. Fiuther reduction of dPSiwith lithium in liquid ammonia and methanol followed by epoxidation afforded 699. Selective oxidation of the more accessible hydroxyl group and phenyl-sulfenylation gave 700 which experiences smooth elimination to 701 after conversion to the sulfoxide. As before, epoxidation completed the sequence. 

Uracils and related pyrimidines undergo oxidative addition to the 5,6-double bond, and the reaction with a number of oxidants to form 5,6-epoxides and 5,6-diols was discussed in CHEC-II(1996) <1996CHEC-II(6)93>. Oxidative halogenation can also occur <1996SC3583, 1998NN1125>, as shown by the formation of 5-bromo-5,6-dihydro-6-methoxyuracil 100 from uracil 99 by treatment with a mixture of potassium bromate and potassium bromide in the presence of Dowex ion-exchange resin in methanol <1996SC3583>. 

The dipole moments of oxepin and benzene oxide have been calculated to be in the range 0.76-1.36 D and >1.5 D respectively using the ab initio SCF and MINDO/3 methods (80JA1255). The lower calculated dipole moment would be in accord with experimental observations where the equilibrium was found to favor oxepin (7) in less polar solvents. Coordination between the oxirane oxygen atom and polar solvent molecules would also strengthen the C—C bond of the epoxide and thus lead to a preference for the benzene oxide isomer <72AG(E)825). Thus the proportion of oxepin (7) was found by UV spectral analysis to be higher in isooctane solvent (70%) than in water-methanol (10%). 

Reduction of epoxides. Epoxides can be reduced by slow addition of methanol to a refluxing mixture of the epoxide and NaBH4 in (-butyl alcohol. The more substituted alcohol is formed preferentially. Presumably the actual reducing agent is NaBH4. n(OCH3)n. Amide, nitro, and nitrile groups are not reduced by the procedure. 

A mixture consisting of 3 g of l-(3-amino-3,3-dimethyl-n-propyl) benzimidazolidinone-2, 3.3 g of l-[naphthyl-(l)-oxyl]propylene-(2,3)-epoxide and 12 ml of 98% ethanol were refluxed for three hours. Thereafter, the ethanol was distilled off, the residue was taken up in some methanol, and the solution was acidified with 1 N hydrochloric acid and then extracted with ethyl acetate. The ethyl acetate was distilled out of the extract solution, and ether and some water were added to the residue, whereupon a crystalline substance separated out. The product was recrystallized from ethanol, yielding 60% of theory of ()-l-(3-((2-hydroxy-3-(l-naphthyloxy)propyl)amino)-3-methylbutyl)-2-benzimidazolinone, which had a melting point of 161°C. 

Li J, Wang L, Liu S et al (2010) MCM-41 grafted quaternary ammonium salts as recyclable catalysts for the sequential synthesis of dimethyl carbonate from epoxides, C02, and methanol. Chem Lett 39 1277-1278... 

Tian J-S, Wang J-Q, Chen J-Y et al (2006) One-pot synthesis of dimethyl carbonate catalyzed by n-Bu4NBr/n-Bu3N from methanol, epoxides, and supercritical C02. Appl Catal A-Gen 301(2) 215-221... 

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