Allyl carbonates carbonylation

Allylic carbonates are most reactive. Their carbonylation proceeds under mild conditions, namely at 50 C under 1-20 atm of CO. Facile exchange of CO2 with CO takes place[239]. The carbonylation of 2,7-octadienyl methyl carbonate (379) in MeOH affords the 3,8-nonadienoate 380 as expected, but carbonylation in AcOH produces the cyclized acid 381 and the bicyclic ketones 382 and 383 by the insertion of the internal alkene into Tr-allylpalladium before CO insertion[240] (see Section 2.11). The alkylidenesuccinate 385 is prepared in good yields by the carbonylation of the allylic carbonate 384 obtained by DABCO-mediated addition of aldehydes to acrylate. The E Z ratios are different depending on the substrates[241]. 

Some organosilicon compounds undergo transmetallation. The allylic cyanide 461 was prepared by the reaction of an allylic carbonate with trimethylsi-lyl cyanide[298]. The oriho esters and acetals of the o. d-unsaturated carbonyl compounds 462 undergo cyanation with trimefhylsilyl cyanide[95]. 

Regio- and Stereoselectivity. For the allylation of carbonyl compounds mediated by indium and other compounds in aqueous media, usually the carbon-carbon bond forms at the more substituted carbon of the allyl halide, irrespective of the position of halogen in the starting material. However, the carbon-carbon bond forms at the less-substituted carbon when the y-substituents of allyl halides are large enough (e.g., trimethylsilyl or tert-butyl) as shown by Chan et al.139 (Scheme 8.10). The following conclusions can be drawn ... 

Tsuji and co-workers carbonylated a-carbonate-substituted allenes 113 with carbon monoxide and methanol, which provided 114 in excellent yields (Scheme 14.25) [54], They found that allenylic carbonates are more reactive than simple allylic carbonates and that the reaction proceeded rapidly even at ambient temperature under atmospheric pressure of carbon monoxide. Unfortunately, the poor E/Z selectivity diminishes the synthetic value of this very efficient carbonylation reaction. 

This electrochemical oxidation mediated by NHPI was applicable to benzylic carbons, allylic carbons, deprotection of acetals, oxidative cleavage of cyclic acetals and amide to afford benzoylated compounds, enones ", carbonyl compounds, -hydroxyethyl esters and imides, respectively (equations 31-35). 

Type IV (spectators to CM) 1,1-Disubstituted olefms " 1,1-Disubstituted olefms, disub. o ,/ -unsaturated carbonyls, 4° allylic carbon-containing olefins, perfluorinated alkane olefins, 3° allylamines (protected)" Vinyl nitro olefins, protected trisubstituted allyl alcohols, a,/ -olefin of 2-subst. 1.3- butadienes, a,/ -olefm of electronically deactivated 1.3- butadienes ... 

Preparation of o,/3-Unsaturated Carbonyl Compounds by the Reactions of Silyl End Ethers and End Acetates with Allyl Carbonates... 

Oxidation of the allylic carbon of alkenes may lead to allylic alcohols and derivatives or a, 3-unsaturated carbonyl compounds. Selenium dioxide is the reagent of choice to carry out the former transformation. In the latter process, which is more difficult to accomplish, Cr(VI) compounds are usually applied. In certain cases, mixture of products of both types of oxidation, as well as isomeric compounds resulting from allylic rearrangement, may be formed. Oxidation of 2-alkenes to the corresponding cc,p-unsaturated carboxylic acids, particularly the oxidation of propylene to acrolein and acrylic acid, as well as ammoxidation to acrylonitrile, has commercial importance (see Sections 9.5.2 and 9.5.3). 

Methylmagnesium N-cyclohexyliso-propylamide, 189 By oxidation at an allylic carbon Selenium dioxide, 272 By reduction of a,0-unsaturated carbonyl compounds Sodium borohydride, 278 Sodium dithionite, 281 Other methods r-Butyllithium, 58 Butyllithium-Potassium f-butoxide,... 

Decarboxylation-carbonylation fS,y-unsaturated esters. Allylic carbonates undergo decarboxylation-carbonylation in the presence of this palladium catalyst at 50° under 10 atms of CO to give /l,y-un saturated esters in 70-95% yield.1 Example ... 

Bis(methylene)butanedioate 68, which is an interesting derivative of butadiene as well as acrylate, can be prepared by the dicarbonylation of the dicarbonate of butynediol 64 [16]. The monocarbonylation of 64 affords the allylic carbonate 65, and the diester 68 is obtained by further carbonylation of n- or cr-allyl complexes 66 and 67. 

Allylation of carbonyl or inline functions is an important carbon-carbon bond forming methodology that also adds functionality for further elaboration and offers... 

Ruthenium complexes are also suitable catalysts for carbonylation reactions of a variety of substrates. Indeed, when a reaction leads to C-Ru or het-eroatom-Ru bond formation in the presence of carbon monoxide, CO insertion can take place at the coordinatively unsaturated ruthenium center, leading to linear ketones or lactones. Thus, ruthenium-catalyzed carbonylative cyclization was involved in the synthesis of cyclopentenones by reaction of allylic carbonates with alkenes in the presence of carbon monoxide [124] (Eq. 93). 

Indium-mediated Barbier-type coupling between carbonyl compounds and allyl halides has been revealed to proceed effectively in diverse reaction media. Even under solvent-free conditions, allylation works well, although no reaction is observed with benzyl bromide and a-halo carbonyl compounds.59 Various aldehydes react with allyl bromide mediated by indium in liquid carbon dioxide to give homoallylic alcohols (Scheme 1). In contrast to the corresponding neat allylation, the liquid C02-mediated reaction can allylate solid aldehydes successfully.60 Indium-mediated allylations of carbonyl compounds with allyl bromide proceed in room temperature ionic liquids. In [bmim][BF4] and [bmim][PF6] (bmin l-butyl-3-methylimidazolium), the desired homoallylic alcohols are formed with good levels of conversion.61 Homoallyllic alcohols are also prepared by the reaction of resin-bound aldehydes (Equation (l)).62... 

The stereochemical outcome can be rationalized by considering the approach of the aldehyde to the preferred conformation of the allylindium. The approach of the aldehyde is postulated to be in antiperiplanar to the OPG group as for the Felkin-Anh model. The allylindium prefers to adopt the conformation 12 rather than 13, where the 1,3-allylic strain with R is minimized and the steric interaction with the aldehyde is also reduced (Scheme 18). The facial selection with respect to the aldehyde is determined by the aldehyde residue (R ) to occupy in the least sterically demanding position, away from the substituted allylic carbon. The carbonyl allylation then proceeds via a six-membered chairlike transition state, in which the aldehyde substitutent attains an equatorial position, to afford the 1,4-syn product. 

As represented in Fig. 166, ring closure to y-piperidonc may occur, starting both from precursors 442 and aminoketones 443 with the suitable aldehyde. The synthesis of aconitine-type diterpene alkaloids" takes place similarly (Fig. 167), the only difference being the presence in the reactive site of an allylic carbon atom (446) instead of the alkyl group in a position to the carbonyl. 

The model correctly predicts (rationalizes) the observed preference for formation of Ae anti raAer than Ae syn product in the cycloaddition reactions of a wide variety of chiral allylic eAers, Aus successfully laying to rest years of frustrated discussion. - It also correctly predicts Aat as Ae size of R increases (Me - Ph < Et < Pr < Bu ), Ae preference for transition state structure (18 ) should increase leading to enhanced anti stereoselectivity (Table 15). At first, Ais prediction seems strange. However, once it is realized Aat, like Ae Felkin-Anh model for nucleophilic addition to a carbonyl, Ae outside position is actually more sterically demanAng Aan Ae inside, Aen Ae prediction is sensible on purely steric grounds. Thus, Ae angle d approach of Ae nitrile oxide oxygen to Ae alkene actually places it nearer Ae outside Aan Ae inside substituent located at Ae allylic carbon. ... 

Ruthenium-catalyzed carbonylations of allylic compounds [62] were described in Chapter 11. Here, ruthenium-catalyzed carbonylative cyclization of allylic carbonates with alkenes, not alkynes, which offers a new route to cyclopentenones is revealed [63]. Treatment of allyl methyl carbonate with 2-norbornene in the presence of 2.5 mol% [RuCl2(CO)3]2 and 10 mol% Et3N in THE at 120°C for 5 h under 3 atm of carbon monoxide gave the corresponding cyclopentenone, exo-4-methyltri-cyclo[5.2.1.0 ]dec-4-en-3-one, in 80% yield with high stereoselectivity exo 100%) (Eq. 5.37). 

Asymmetric allylation of carbonyl substrates and their derivatives is currently of particular interest in the synthesis of a wide range of optically active compounds, owing to the easy derivatization of the carbon-carbon double bond to a desired functional group. The strategy for reaching this goal can be classified into three approaches ... 

In an imaginative construction of the angular triquinane ( )-hirsutene (158), Oppolzer and Robyr reported the carbonylative closure of allylic carbonate 155 to yield bicyclooctanes 156 and 157 (Scheme 6-27) [57]. In this multistep transformation, a alJylpalladium intermediate arising from the allylic carbonate 155 undergoes intramolecular Heck insertion of the pendant alkyne. Carbonylation of the resulting vinylpalladium intermediate, another Heck cyclization, and a second carbonylation then provide a mixture of acids, which after esterification yield esters 156 and 157 in good yield. 

A six-membered cyclic allylic carbonate 102 undergoes a palladium-catalyzed decarboxylative C-C bond cleavage to afford dienic carbonyl compound 104 [122]. Decarboxylation of the allylic carbonate moiety provides the driving force for production of the intermediate five-membered hetero-palladacycle 103, from which formal reductive cleavage takes place. 

Allylic carbonates [46],acetates [47,48], ethers [49,50],alcohols [51,52],and phosphates [53] have been employed for catalytic carbonylation by using palladium complexes. Pd-catalyzed conversion of allylic formates into carboxylic acids has been also achieved recently [54]. 

In the past decade much effort in organoindium chemistry has been devoted to study of carbonyl allylation and aUylindation of carbon-carbon multiple bonds with allylic indium reagents. Apart from the conventional transmetalation of allyl-lifhium or aUyl Grignard reagents with indium(III) halides, a method widely used for preparation of allyhndium(III) compounds is the oxidative addition of metallic indium or indium(I) iodide to aUyhc substrates [3, 6]. Transmetalation of allylstan-nane with indium(III) chloride also gives allylindium(III) [7]. Allylindium(I) was recently prepared by transmetalation of allylmercury with metallic indium in water this compound is regarded as an intermediate in the allylation of carbonyl compounds in aqueous media [8]. A new method of preparation of allylic in-dium(III) reagents - reductive transmetalation of a 7r-allylpalladium(ll) complex with indium(I) salts has been reported this enables the use of a wide variety of allylic compounds and solvents [9]. 

Allylation and propargylation of carbonyl compounds have been surveyed [5]. This section focuses on regio- and stereochemical aspects of the carbonyl allylation reactions in organic and aqueous media. Allylation of carbonyl compounds also proceeds under solvent-free conditions [10] or in liquid carbon dioxide [11]. Allylation with a catalytic amount of indium (0.01-0.1 equiv.) in combination with manganese and chlorotrimethylsilane has been reported [12]. Allylindium reagents have successfully been applied to syntheses of several natural products [13]. 

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