Allyl methyl carbonate

Another preparative method for the enone 554 is the reaction of the enol acetate 553 with allyl methyl carbonate using a bimetallic catalyst of Pd and Tin methoxide[354,358]. The enone formation is competitive with the allylation reaction (see Section 2.4.1). MeCN as a solvent and a low Pd to ligand ratio favor enone formation. Two regioisomeric steroidal dienones, 558 and 559, are prepared regioselectively from the respective dienol acetates 556 and 557 formed from the steroidal a, /3-unsaturated ketone 555. Enone formation from both silyl enol ethers and enol acetates proceeds via 7r-allylpalladium enolates as common intermediates. 

The slow oxidation of primary alcohols, particularly MeOH, is utilized for the oxidation of allylic or secondary alcohols with allyl methyl carbonate without forming carbonates of the alcohols to be oxidized. Allyl methyl carbonate (564) forms 7r-allylpalladium methoxide, then exchange of the methoxide with a secondary or allylic alcohol 563 present in the reaction medium takes place to form the 7r-allylpalladium alkoxide 565, which undergoes elimination of j3-hydrogen to give the ketone or aldehyde 566. The lactol 567 was oxidized selectively with diallyl carbonate to the lactone 568 without attacking the secondary alcohol in the synthesis of echinosporin[360]. 

A solution of Pd(OAc)2 (0.1 mmol), the ketene acetal (lmmol) and allyl methyl carbonate (2 mmol) in MeCN (5 ml) was heated under reflux for 2-6h, the course of reaction being monitored by t.l.c. or g.l.c. analysis. On completion, the cooled reaction solution was filtered through fluorosil. The... 

In the presence of copper and palladium catalysts, terminal alkynes 1222 react with trimethylsilyl azide and allyl methyl carbonate to provide 2,4-disubstituted 1,2,3-triazoles 1223 in moderate to good yield. Isomerization of the allyl substituent in the presence of a ruthenium catalyst gives 4-substituted 2-(l-propen-l-yl)-2//-l,2,3-triazoles 1224. 

The scope of allylic electrophiles that react with amines was shown to encompass electron-neutral and electron-rich ciimamyl methyl carbonates, as well as furan-2-yl and alkyl-substituted allylic methyl carbonates. An ort/io-substituted cinnamyl carbonate was found to react with lower enantioselectivity, a trend that has been observed in later studies of reactions with other nucleophiles. The electron-poor p-nitrocinnamyl carbonate also reacted, but with reduced enantioselectivity. Allylic amination of dienyl carbonates also occur in some cases with high selectivity for formation of the product with the amino group at the y-position over the s-position of the pentadienyl unit [66]. Arylamines did not react with allylic carbonates under these conditions. However, they have been shown to react in the presence of the metalacyclic iridium-phosphoramidite catalysts that are discussed in Sect. 4. 

Palladium-mediated cydization based on the reactivity of o-alkynyl or alkenyl-phenyl isonitriles have been developed [105]. On the basis of their earlier studies on the three-component synthesis of allyl aryl cyanamides [106], Yamamoto and co-workers reported a palladium-catalyzed three-component coupling reaction of 2-alkynylisocyanobenzenes 122 with allyl methyl carbonate and trimethylsilylazide leading to N-cyanoindoles 125 [107]. One of the key steps of the proposed mechanism is the formation of 7i-allylpalladium carbodiimide 123 and its isomerization to rc-allylpalladium cyanamide complex 124 (Scheme 8.50). 

Although simple ketones and esters can not be allylated by Pd catalysts, they are allylated with allyl carbonates via their enol ethers of Si and Sn. In the allylation of the silyl enol ether 202 with allyl carbonate 200, transmetallation of 202 with the n-allylpalladium methoxide 201, generated from allyl methyl carbonate (200), takes place to generate the Pd enolates 203 and 204. Depending on the reaction conditions, allyl ketone 205 is formed by the reductive elimination of 203 [100]. When the ratio of Pd Ph3P is small, the a,/i-unsaturated ketone 206 is obtained by -elimination [101]. For example, the silyl enol ether 208 of aldehyde 207 is allylated with allyl carbonate (200) to give a-allylaldehyde 210 via 209. The a-allyl carboxylate 213 is obtained by allylation of ester 211 with allyl carbonate (200), after conversion of ester 211 to the ketene silyl acetal 212 [102], As the silyl group is trapped in these... 

We reported that the palladium-catalyzed three-component coupling reaction of the activated alkynes 41, allyl methyl carbonate 5b, and trimethylsilyl azide 42 gave the 2-allyl-1,2,3-triazoles 43. The reaction proceeds via the [3 + 2] cycloaddition of tt-allylpalladium azide 44 to the alkynes 41, followed by the formation of (-allyl)(r]5-triazoyl)-palladium 45 (Scheme 16) [51]. However, this method was limited only for activated alkynes. Synthesis of the triazoles 47 from the nonactivated terminal alkynes 46 was achieved by the three-... 

The selective synthesis of the 2-allyltetrazoles 55 by the three-component coupling reaction of the cyano compounds 54, allyl methyl carbonate 5b, and trimethylsilyl azide 42 was accomplished in the presence of Pd2(dba)3.CHCl3 and P(2-furyl)3 (Scheme 19) [55,56]. Most probably, the formation of (r)3-allyl)( ]5-tetrazoyl)-palladium complex 56 took place through [3 + 2] dipolar cycloaddition of 7r-allylpalladium azide 44 with the nitrile 54. The complex 56 thus formed would undergo reductive elimination to form the products 55. 

Triazole derivatives could be synthesized from different starting substrates. Various triazoles 155 were synthesized from nonactivated terminal alkynes 152, allyl methyl carbonate 153 and trimethylsilyl azide 154 in a [3 + 2] cycloaddition with the use of the Pd(0)-Cu(I) bimetallic catalyst <03JA7786>. The allyl group of 155 was efficiently deprotected by ruthenium-catalyzed isomerization followed by ozonolysis to give 4-substituted triazoles 156. a-Aminoacetophenones 157 were reacted with hydrazines in acetic acid to give an efficient... 

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). 

Kamijo and Yamamoto developed a palladium-catalyzed three-component synthesis of N-cyanoindoles (131) (Scheme 5.39) [81]. The reaction of a 2-alkynyliso-cyanobenzene (132), allyl methyl carbonate, and trimethylsilylazide in the presence of Pd2(dba)3 (2.5 mol%) and tri(2-furyl)phosphine (10 mol%) at 100 °C afforded the N-cyanoindoles 131 in good yield. Key steps of this reaction involved the formation of jt-allylpalladium complex 133, its Curtius-like rearrangement to intermediate 134, and subsequent isomerization to the Jt-allylpalladium cyanamide complex 135. A wide range of functional groups is tolerated at the para, meta, and even ortho positions of the aromatic ring. 

The bis-allylation reaction has been extended to the reaction of heteroatom-containing bis-jr-allylpalla-dium analogues. We demonstrated that the palladium-catalyzed three-component coupling reaction of the 2-alkynylisocyanobenzenes 646, allyl methyl carbonate, and trimethylsilyl azide gave the N-cyanoindoles 647 in good yields (Scheme 201).278 This... 

Allylic substitutions. The TT-allylpalladium ions are electrophilic agents. Dial-lylation of (benzothiazol-2-ylthio)methyl ketones is readily achieved using allyl methyl carbonate as reaction partner. The generation of a Pd-complexed trimethylene-methane from 2-(trimethylsilylmethyl)allyl esters is well known the interception of this species by imines gives 3-methylenepyrrolidines. ... 

Finally, Yamamoto has recently reported the cross-coupling of a silylalkyne, allyl methyl carbonate, and trimethylsilyl azide to produce a diallyltriazole (Eq.90) [160]. 

Leitner and co-workers described Pd-catalyzed nucleophilic substitutions ofallylic substrates with different nucleophiles [27]. They used Pd2(dba)3 as the palladium source and phosphane 20 as perfluoro-tagged ligand [Eq. (5)]. Reaction between cinnamyl methyl carbonate (21) and various nucleophiles (Nu-H) were performed in a THF/C7FJ4 biphasic mixture. A decrease in conversion was observed only after the ninth run (with 5 mol% Pd complex). By reducing the amoimt of Pd complex to 1 mol%, five quantitative recyclings were possible. The standard protocol was also applied to the condensation of dimethyl malonate with allyl methyl carbonate, (2-vinyl)butyl carbonate, and cyclohex-2-enyl carbonate. In each case two recyclings were performed without any decrease in conversion. 

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