Homoallyl chloroformates

The acylpalladium complex formed from acyl halides undergoes intramolecular alkene insertion. 2,5-Hexadienoyl chloride (894) is converted into phenol in its attempted Rosenmund reduction[759]. The reaction is explained by the oxidative addition, intramolecular alkene insertion to generate 895, and / -elimination. Chloroformate will be a useful compound for the preparation of a, /3-unsaturated esters if its oxidative addition and alkene insertion are possible. An intramolecular version is known, namely homoallylic chloroformates are converted into a-methylene-7-butyrolactones in moderate yields[760]. As another example, the homoallylic chloroformamide 896 is converted into the q-methylene- -butyrolactams 897 and 898[761]. An intermolecular version of alkene insertion into acyl chlorides is known only with bridgehead acid chlorides. Adamantanecarbonyl chloride (899) reacts with acrylonitrile to give the unsaturated ketone 900[762],... 

Homoallyl chloroformates cyclize catalytically to a-methylene- y-butyrolactones in moderate yields at 130 C with tetrakis(triphenylphosphine)palladium(0) (equation 44).l0s This reaction only gives 1-2% of product when it is carried out intermolecularly. The presumed intermediate in the homoallyl chlorofor-mate cyclization has been isolated and kinetic measurements show that that cyclization is inhibited by an excess of triphenylphosphine. A chelated ir-alkene intermediate is proposed.1 6... 

Cho et al. reported a indium trichloride-catalyzed intramolecular Prins-type reactions of compounds having both the functionalities of homoallyl alcohol and acetal moiety. The intramolecular Prins cycliza-tions were performed using indium trichloride in chloroform or 25%... 

Starting from 2,4,6-octatriene and pivaldehyde, the conjugated homoallylic alcohol 8 is obtained as the sole product. Cycloheptatriene-derived complexes react with aldehydes and C02 to afford mixtures of the isomeric 1,3- and 1,4-cycloheptadienyl carbinols or acids, respectively. Interestingly, analogous reactions with methyl chloroformate or dimethyl carbamoyl chloride produce the conjugated dienyl ester 9 or amide 10 as unique products [19,20]. 

In another example, a catalytic amount of cerium triflate hydrate was dispersed and isolated in [BMIMJPFg for the direct formation of tetrahydropyranol derivatives. The reaction involves a simple homoallyl alcohol and an aldehyde. When an organic solvent such as chloroform was employed, an undesired ether derivative formed as the major product. In the ionic liquid, however, the desired tetrahydropyranol was exclusive. Although the yield was moderate, this example constitutes the first relatively facile and direct formation of the synthetically useful pyranol derivative the only effective catalyst reported is the ionic liquid (168). 

The synthesis of tctrahydropyranols from the reaction between an aldehyde and a homoallylic alcohol with catalytic amounts of Ce(OTf)3 immobilised in [C4Ciim][PF6] affords the desired product in moderate yield after 12 hours at room temperature, see Scheme 9.18.[64] Addition of one equivalent of benzoic acid as co-catalyst was found to increase the isolated yield, but its role is not yet clear. A beneficial effect of performing the reaction in the ionic liquid is that, contrary to the reaction in chloroform, no ether derivatives were observed. 

TTOC Carbonates To a cold solution (0 C) of 23 mmol of phosgene in 12 mL of toluene are added 4 mmol of the appropriate allylic or homoallylic alcohol and 0.43 g (3.3 mmol) of triethylamine. After 2 h at 0 °C, excess phosgene and solvents are removed at reduced pressure. The crude chloroformate is dissolved in 30 mL of benzene and to this solution is added a mixture of 0.4 g (4 mmol) of 3-hydroxy-4-methylthiazolc-2(3//)-thione and 0.43 g (4.3 mmol) of triethylamine in 5 mL of benzene. After 3 h at 20 °C, the solvent is removed under reduced pressure, and the crude TTOC carbonate is purified by chromatography (silica gel, EtOAc/hexane 15 85). The TTOC carbonates are isolated in 60- 65% yield and can be employed in subsequent reactions without purification. 

In a diastereoselective modification of this reaction, the imidates 7 were prepared starting from primary allylic and homoallylic alcohols and the nitrile 6 following a standard procedure1 sfi. By cyclization of 7 with A -iodosuccinimide in chloroform at 20 °C, diastereomeric mixtures were obtained with one diastereomer predominating, which was easily separated. The configuration of the diastereomer was assigned on the basis of X-ray analysis. 

Esters of allylic and homoallylic alcohols undergo addition of dichlorocarbene, the reactions are conveniently carried out by the chloroform/base/phase-transfer catalyst method. Some products of this type are specified in Table 17. 

Dichlorocyclopropanation, using the chloroform/base/phase-transfer catalyst, of homoallylic alcohol 5 gave stereoselectively the product 6, while the same reaction carried out with 7 afforded a mixture of diastereomers 8 and 9. ... 

Vinyl, allyl and homoallyl derivatives of germanium and tin also form the corresponding cyclopropanes with dichlorocarbene generated by the chloroform/potassium /er/-butoxide or bromodichloromethyl(phenyl)mercury methods (Table 23). ... 

With rhodium as transition metal the product formation is strongly dependent on the substitution pattern and the solvent used. With dicarbonylchlororhodium dimer in methanol, 1,2,2-trimethylbicyclo[1.1.0]butane(34, = Me R = H) exclusively affords the cyclopropylmethyl methyl ether 35 in almost quantitative yield. However, when R = Ph and R = H or Me the formation of the homoallylic ether 36 is strongly favored. When an aprotic solvent is used, such as chloroform instead of methanol, no cyclopropylmethyl derivative is obtained. Instead the corresponding diene is isolated. ... 

Homoallylic nitro compounds 845 are accessible by conversion of allylic alcohols to carbonates followed by their palladium-catalyzed solvolysis in nitromethane [618]. Ethoxycarbonylation of the alcohols 843 with ethyl chloroformate provides the corresponding allylic ethyl carbonates in high yields (99% in the case of 844). Exposure of these substrates to catalytic palladium(O) in nitromethane initiates a reaction sequence of ionization - decarboxylation - nitromethylation, which culminates in the formation of nitroalkenes 845. 

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