Alkyl formates, synthesis

The procedure described is essentially that of Shioiri and Yamada. Diphenyl phosphorazidate is a useful and versatile reagent in organic synthesis. It has been used for racemlzatlon-free peptide syntheses, thiol ester synthesis, a modified Curtius reaction, an esterification of a-substituted carboxylic acld, formation of diketoplperazines, alkyl azide synthesis, phosphorylation of alcohols and amines,and polymerization of amino acids and peptides. - Furthermore, diphenyl phosphorazidate acts as a nitrene source and as a 1,3-dipole.An example in the ring contraction of cyclic ketones to form cycloalkanecarboxylic acids is presented in the next procedure, this volume. 

This is clo.sely related to the Tertiary radical synthesis" scheme for the preparation of organocobalt porphyrins, in which alkenes insert into the Co—H bond of Co(Por)H instead of creating a new radical as in Eq. (13). If the alkene would form a tertiary cobalt alkyl then polymerization rather than cobalt-alkyl formation is observed. " " " The kinetics for this process have been investigated in detail, in part by competition studies involving two different alkenes. This mimics the chain transfer catalysis process, where two alkenes (monomer and oligomers or... 

Other mechanisms for the synthesis of alkylformates, not via formic acid esterification, are possible. Hydrogenation of C02 to CO, followed by catalytic car-bonylation of alcohol, would produce alkyl formate. This mechanism seems more likely for the anionic metal carbonyls because they are known catalysts for alcohol carbonylation. However, Darensbourg and colleagues [64, 74, 85] showed... 

Preparation of formamides from COz and a non-tertiary amine by homogeneous hydrogenation has been well studied and is extremely efficient (Eq. (12)). Essentially complete conversions and complete selectivity can be obtained (Table 17.3). This process seems more likely to be industrialized than the syntheses of formic acid or formate esters by C02 hydrogenation. The selectivity is excellent, in contrast to the case for alkyl formates, because the amine base which would stabilize the formic acid is used up in the synthesis of the formamide consequently little or no formic acid contaminates the product. The only byproducts that are likely to crop up in industrial application are the methylamines by overreduction of the formamide. This has been observed [96], but not with such high conversion that it could constitute a synthetic route to methylamines. 

Skeletal Cu-Zn catalysts show great potential as alternatives to coprecipitated Cu0-Zn0-Al203 catalysts used commercially for low temperature methanol synthesis and water gas shift (WGS) reactions. They can also be used for other reactions such as steam reforming of methanol, methyl formate production by dehydrogenation of methanol, and hydrogenolysis of alkyl formates to produce alcohols. In all these reactions zinc oxide-promoted skeletal copper catalysts have been found to have high activity and selectivity. 

In 1970 the transition metal catalyzed formation of alkyl formates from CO2, H2, and alcohols was first described. Phosphine complexes of Group 8 to Group 10 transition metals and carbonyl metallates of Groups 6 and 8 show catalytic activity (TON 6-60) and in most cases a positive effect by addition of amines or other basic additives [26 a, 54-58]. A more effective catalytic system has been found when carrying out the reaction in the supercritical phase (TON 3500) [54 a]. Similarly to the synthesis of formic acid, the synthesis of methyl formate in SCCO2 is successful in the presence of methanol and ruthenium(II) catalyst systems [54 b]. 

Pirrung, M. C., Wedel, M., Zhao, Y. 7-Alkyl indole synthesis via a convenient formation/alkylation of lithionitrobenzenes and an improved Bartoli reaction. Syniett 2002, 143-145. 

Our recent interest in the chemistry of carbon dioxide (9,12) has included investigations of the synthesis of alkyl formates utilizing CO2 as a source of chemical carbon (Equation 7) (47,48). 

Several processing alternatives have been proposed for converting synthesis gas to methanol. The main incentives are reduced energy costs due to the ability to operate at lower temperatures, lower pressures or both. The most notable of these alternatives (in terms of recent interest) have been the alkyl formate process (ref. 27) and the Chem Systems three-phase reactor approach (ref. 28). A very recent development is the use of a gas-solid-solid trickle flow reactor.which it is proposed can be retrofitted in conventional low pressure methanol synthesis plants (ref. 29). These three alternatives will be reviewed in turn. 

The synthesis of methanol via an alkyl formate was proposed as early as 1919 (ref. 30). In this process an alcohol is first carbonylated to its formate ester according to ... 

Support for Methanol Synthesis research involving Raney copper-zinc catalysts and alkyl formates was provided under the National Energy Research Development and Demonstration Program administered by the Commonwealth Department of National Development. 

The synthesis of homologues of (hydroxymethylene)bisphosphonic acid may be achieved through reactions between other carboxylic acids, PCI3 and water at 130 and the use of carboxylic esters is also feasible". (Hydroxymethylene)bisphosphonic acid and its ethers are obtainable from tetraalkyl pyrophosphites and alkyl formates in the presence of BF3 at 20-130 Yet a further reactant combination consists of an alkanoic ester, and P4O6-BF3, which produces glasses, but from which the bisphosphonic acid may be extracted with boiling dilute HCl. ... 

Controlled hydrolysis of diorganotin dihalides leads to dimeric tetraorganodistannoxanes [R2(X)SnOSn(X)R2]2 (R = alkyl, aryl X = halogen, OH) [1, 2]. These compounds hold potential as efficient homogeneous catalysts in various organic reactions, e.g. transesterification [3], urethane formation [4], and alkyl carbonate synthesis [5]. 

SYNTHESIS OF KETONES VIA a-ALKYLATION Formation and Reactivity of Enolates... 

The synthesis of organic amides from carboxylic esters is a general synthetic transformation, which, in many cases, necessitates drastic conditions (high temperature, increase of reaction time) or the use of catalysts. This process is a potentially attractive and its various aspects are studied for many years (see, for example, (107,108)]. The action of alkyl formates on N-silymethylamines leads to acylation to deliver N-silylmethylformamides (Scheme 24.19) (109). These reactions... 

The formation of the above anions ("enolate type) depend on equilibria between the carbon compounds, the base, and the solvent. To ensure a substantial concentration of the anionic synthons in solution the pA" of both the conjugated acid of the base and of the solvent must be higher than the pAT -value of the carbon compound. Alkali hydroxides in water (p/T, 16), alkoxides in the corresponding alcohols (pAT, 20), sodium amide in liquid ammonia (pATj 35), dimsyl sodium in dimethyl sulfoxide (pAT, = 35), sodium hydride, lithium amides, or lithium alkyls in ether or hydrocarbon solvents (pAT, > 40) are common combinations used in synthesis. Sometimes the bases (e.g. methoxides, amides, lithium alkyls) react as nucleophiles, in other words they do not abstract a proton, but their anion undergoes addition and substitution reactions with the carbon compound. If such is the case, sterically hindered bases are employed. A few examples are given below (H.O. House, 1972 I. Kuwajima, 1976). 

In the prostaglandin synthesis shown, silyl enol ether 216, after transmetaJ-lation with Pd(II), undergoes tandem intramolecular and intermolecular alkene insertions to yield 217[205], It should be noted that a different mechanism (palladation of the alkene, rather than palladium enolate formation) has been proposed for this reaction, because the corresponding alkyl enol ethers, instead of the silyl ethers, undergo a similar cyclization[20I],... 

Alkene synthesis via alcohol dehydration is complicated by carbocation rearrangements A less stable carbocation can rearrange to a more sta ble one by an alkyl group migration or by a hydride shift opening the possibility for alkene formation from two different carbocations... 

A method that achieves the same end result as that desired by alkylation of ammonia but which avoids the formation of secondary and tertiary amines as byproducts is the Gabriel synthesis Alkyl halides are converted to primary alkylamines without contam mation by secondary or tertiary amines The key reagent is the potassium salt of phthal imide prepared by the reaction... 

Among compounds other than simple alkyl halides a halo ketones and a halo esters have been employed as substrates m the Gabriel synthesis Alkyl p toluenesul fonate esters have also been used Because phthalimide can undergo only a single alkyl ation the formation of secondary and tertiary amines does not occur and the Gabriel synthesis is a valuable procedure for the laboratory preparation of primary amines... 

Gabriel synthesis (Section 22 8) Method for the synthesis of primary alkylamines in which a key step is the formation of a carbon-nitrogen bond by alkylation of the potassium salt of phthalimide... 

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