Allyl hydrogenolysis

However, there is no reason to believe that a x-allyl or x-olefin mechanism for C—C bond rupture is limited to ring opening. Rather it should be a general process occurring in straight and branch-chain aliphatics as well. For the purpose of illustration, we write reactions (22) and (23) as generalizations of the reverse of (11) and (13), respectively. We shall refer to mechanisms such as (22) and (23) x-olefin/allyl hydrogenolysis... 

With catalysts such as nickel and rhodium for which it has been shown that 1-2 hydrogenolysis is seriously competitive with 1-3 hydrogenolysis, there is no need to assume that ir-olefin/allyl hydrogenolysis occurs (but neither can it with certainty be excluded). This conclusion is likely to be true for other catalysts such as cobalt and iron which also favor complete hydrocarbon fragmentation to methane. 

The simplest case is that of the ATb-methylstrychninium ion with palladium as a catalyst, the acetate undergoes normal allylic hydrogenolysis to give XC as the main product, together with small quantities... 

Hydrogenolysis of isostrychnine methochloride (XCV R = H) and isopseudostrychnine methochloride (XCV R = OH) leads to the same product (XCVI) (95, 96). On the other hand, 0-methyl pseudostrychnine metho salt (XCVII R = H) gives mainly the corresponding quaternary dihydro derivative, and only a small yield of base XCVIII (R = H) (97). Allylic hydrogenolysis, however, again predominates in the case of... 

The zwitterionic form CCVII is also believed to be responsible for the allylic hydrogenolysis of V-methyl-sec-isopseudostrychnine (CXXII) to XCVI (95) and for the failure of CXXII to be reduced at C-16 by lithium aluminum hydride. 

The sodium amalgam (Emde) reduction of vomicine metho salts (CCLIV) in dilute acetic acid gives two products (195, 203) base I, which has structure CCLVII (R = CH3) (202), and base II, the structure of which is not proved (202, 203). Why allylic hydrogenolysis does not occur is not known. Base I is demethylated to a secondary alcohol CCLVII (R = H) (203), which could not be oxidized by the Oppenauer method back to vomicine (202), nor could vomicine be reduced to it. 

Catalytic hydrogenolysis of methyl vomicinium salts leads to a mixture of the corresponding dihydrovomicinium quaternary salt and of two isomeric tertiary bases, probably epimeric at C-21, to which structure CCLX has been given (195, 202). The reduction in this case then proceeds by way of a normal allylic hydrogenolysis, and is to be contrasted with the abnormal Na/Hg reduction. 

An alternative formulation for methiodide A, CCLXV (162) accounts for the allylic hydrogenolysis, and requires double-bond migration for the formation of base I, which would have structure CCLXVI base II would have structure CCLXVII, the dihydro derivative of base I would be a stereoisomer of CCLXVIII, as would the hydrogenolysis and Na/Hg reduction product C23H34O3N2. 

Anions of allylic thioethers may also be alkylated with alkyl bromides in high yield. The thioether groups can subsequently be removed by hydrogenolysis (F.W. Sum, 1979). 

The secondary allylic methylamine 324 can be prepared by the allylation of A -methylhydroxylamine (323), followed by hydrogenolysis[201], Monoallylation of hydroxylamine, which leads to primary allylamines, is achieved using the jV,0-bis-Boc-protected hydroxylatnine 326. N -... 

The Pd-catalyzed hydrogenolysis of allylic compounds by various hydrides gives alkenes. From terminal allylic compounds, either 1-alkenes or 2-alkenes are formed depending on the hydride sources [360a]. 

In addition to the preparation of l-alkenes, the hydrogenolysis of allylic compounds with formate is used for the protection and deprotection of carboxylic acids, alcohols, and amines as allyl derivatives (see Section 2.9). 

Various terminal allylic compounds are converted into l-alkenes at room temperature[362]. Regioselective hydrogenolysis with formate is used for the formation of an exo-methylene group from cyclic allylic compounds by the formal anti thermodynamic isomerization of internal double bonds to the exocyclic position[380]. Selective conversion of myrtenyl formate (579) into /9-pinene is an example. The allylic sulfone 580 and the allylic nitro compound... 

As a further application of the reaction, the conversion of an endocyclic double bond to an c.xo-methylene is possible[382]. The epoxidation of an cWo-alkene followed by diethylaluminum amide-mediated isomerization affords the allylic alcohol 583 with an exo double bond[383]. The hydroxy group is eliminated selectively by Pd-catalyzed hydrogenolysis after converting it into allylic formate, yielding the c.ro-methylene compound 584. The conversion of carvone (585) into l,3-disiloxy-4-methylenecyclohexane (586) is an example[382]. 

Asymmetric hydrogenolysis of allylic esters with formic acid with satisfactory ee was observed[387], Geranyl methyl carbonate (594) was reduced to 570 with formic acid using l,8-bis(dimethylamino)naphthalene as a base and MOP-Phen as the best chiral ligand, achieving 85% ee. 

Furthermore, the regioselective hydrogenolysis can be extended to internal allylic systems. In this case, clean differentiation of a tertiary carbon from a secondary carbon in an allylic system is a problem. The regioselectivity in the hydrogenolysis of unsymmetrically substituted internal allylic compounds depends on the nature and size of the substituents. The less substituted alkene 596 was obtained from 595 as the main product, but the selectivity was only... 

The method has been successfully applied to steroids. The fnms AB ring junction in 612 can be generated cleanly from the. i-allylic formate 611 the cis junction in 614 is formed by the hydrogenolysis of the a-allylic formate 613... 

Highly regio- and stereoselective 4a-deuteration in steroids is possible by the hydrogenolysis of the cyclic allylic /3-carbonate 628 with NaBD4. the extent of 6a-deuteration is only 3%[393],... 

The Pd-catalyzed hydrogenolysis of vinyloxiranes with formate affords homoallyl alcohols, rather than allylic alcohols regioselectively. The reaction is stereospecific and proceeds by inversion of the stereochemistry of the C—O bond[394,395]. The stereochemistry of the products is controlled by the geometry of the alkene group in vinyloxiranes. The stereoselective formation of stereoisomers of the syn hydroxy group in 630 and the ami in 632 from the ( )-epoxide 629 and the (Z)-epoxide 631 respectively is an example. 

Allylic amines can be cleaved. Hydrogenolysis of allylic amines of different stereochemistry with NaBH CN was applied to the preparation of both dia-stereoisomers 655 and 657 of cyclopentenylglycine from the cyclic amines 654 and 656 of different stereochemistry[405]. 

Tributyltin hydride is used for hydrogenolysis of allylic esters[369-372]. 

Hydrogenolysis of the diallyl alkylmalonate 757 with formic acid in boiling dioxane affords the monocarboxylic acid 758. Allyl ethyl malonates are converted into ethyl carboxylates[471]. The malonic allyl ester TV-allylimide 759 undergoes smooth deallylation in refluxing dioxane to give the simple imide 760(472]. The allyl cyanoacetate 761 undergoes smooth decarboxylation to give... 

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