Phase transfer hydrogenolysis

The complexes [PdCl2(133)2] catalyze the hydrogenolysis of 1-chloromethylnaphthalene with K[HCOO] or Na[HCOO]. Both the solid methanoates and their aqueous solutions could be used. Addition of [R4N]+X phase transfer agents significantly accelerated the hydrogenolysis of aryl halides with methanoates.347... 

General.—The relatively unreactive diethyl arylmethylphosphonates have been used quite successfully in alkene synthesis with phase-transfer catalysis.100 In a comparative study it was shown that anions derived from /S-ketophosphonamides (109) have very low reactivity whereas those from 0-ketophosphonates (110) react quite well with aldehydes to give frwjj-alkenes.101 Benzyl dimethyl phosphonoacetate (111) can be used to form alkenes, e.g. (112), from which the benzyl group can be removed by hydrogenolysis without disturbing the C=C bond.102 The carbanions (113) can be... 

Rhodium(III) complexes [e.g. (i-Pr,P)2Rh(H)Cl2] in the presence of quaternary ammonium salts are excellent catalysts for the hydrogenolysis of chloroarenes under mild conditions [5] other labile substituents are unaffected. Hydrodehalogenation of haloaryl ketones over a palladium catalyst to give acylbenzenes is also aided by the addition of Aliquat [6]. In the absence of the phase-transfer catalyst, or when the hydrogenation is conducted in ethanol, the major product is the corresponding alkyl-benzene, which is also produced by hydrodehalogenation of the halobenzyl alcohols. 

Hydrogenolysis of vinyl sulfones.2 Vinyl sulfones are reduced by Na2S204 and NaHC03 in aqueous ethanol with retention of configuration. The reaction is facilitated by use of a phase-transfer catalyst such as Adogen. The reduction involves addition of HSOz to form a sulfone sulfinate salt which can be trapped by CH3I. The overall reaction thus involves a (3-syn-addition followed by an anti-elimination. This hydrolysis was used in a synthesis of several insect pheromones, such as (Z)-8-dodecenyl-l-acetate (1). 

The air-sensitive Cp-substituted hydridovanadium complex is obtained by hydrogenolysis of the corresponding methyl derivative. The corresponding anionic compound is obtained by reduction of CpV(CO)4 with sodium and protonation with water (Scheme 64). Thus obtained [CpVH(CO)3] (106) is a useful one-electron reductant to reduce bromo- and iodoalkanes, bromoalkenes, and arylbromides in THF. Furthermore, acid chlorides are reduced to the aldehydes. A similar reduction with (106) is performed by using phase-transfer conditions in the presence of tetrabutylammonium hydrogen sulfate. Nitro compounds and organic halides are reduced under these conditions. 

Bar,R., Y. Sasson, and Y. Blum, Hydrogenolysis of Aryl Bromides by Sodium Formate and Palladium-Phosphone Catalyst Under Phase Transfer Conditions, J.Mol.Catal.,l6, 175 (1982). 

O-Demethylation has been observed as well as, or instead of, nucleophilic displacement on reaction of 3,4,5-chloro/methoxy pyridazines and 4,5-chloro/methoxy-2-methyl-3(2//)-py-ridazinones with morpholine (e.g.. Scheme 63). Demethylation was observed at all ring positions, but usually adjacent to chlorine or a carbonyl group, and A -methylmorpholine was isolated, consistent with demethylation rather than hydrolysis. The demethylation can also occur with other primary and secondary amines such as diethylamine, butylamine, and piperidine, but not with pyrrolidine and aniline <87H(26)1 >. 3-Phenolic ethers of pyridazines are resistant to reductive cleavage of the aryl ether bond under the conditions of phase transfer catalytic hydrogenolysis <82T3775>. 

A new synthesis of 5-chloro-l-phenyltetrazole, a useful activating group for the hydrogenolysis of phenols, was reported using NCS-mediated chemistry. The phase-transfer reaction of NCS with sodium azide in chloroform generates chloroazide in situ. The transient chloroazide reacts with phenyl isocyanide via a 1,3-dipolar cycloaddition at 0 °C to afford 5-chloro-l-phenyltetrazole in 69% yield (eq 30). ... 

Since most of the phase transfer reactions useful for synthesis are reviewed in Ch. 4, this section will contain only a few examples of hydrogenation or hydrogenolysis on metallic catalysts. 

P (p-anisyl)3 >> PMePh2, dppe) whose activities decrease with increasing ligand basicity as shown . The hydrogenolysis of aryl bromides by benzyl alcohol is catalysed by a Pd(II) complex under phase transfer conditions (reaction 2) . 

Quaternary ammonium salts aid the transfer of the hypophosphite anion in the palladium-catalysed reduction of, for example, alkynes to alkenes, nitroarenes to aminoarenes, and in the hydrogenolysis of tetrazolyl aryl ethers to phenols [12-14], It has been demonstrated that the hydrogenolysis is ineffective when preformed tetra-n-butylammonium hypophosphite is employed in a dry homogenous organic solvent [13, 14], For optimum hydrogen transfer, the concentration of hypophosphite relative to the substrate must be controlled at a low level and this is most effectively accomplished with a two-phase system. 

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