Alkylation, mechanism with allyl alcohol

Evans and Nelson examined the stereospecificity of the rhodium-catalyzed allylic alkylation, with the expectation that it would provide additional insight into the mechanism for this particular reaction [16]. They reasoned that the enantiomerically enriched allylic alcohol derivative i would furnish the enantioenriched product iv, provided the initial enyl intermediate ii does not isomerize to the achiral rr-organorhodium intermediate iii prior to alkylation (k2>ki Scheme 10.3). Alternatively, the product of re-... 

The reaction of perfluoroalkyl iodides with alkenes affords the perfluoro-aikyiated alkyl iodides 931. a.a-Difluoro-functionalized phosphonates are prepared by the addition of the iododifluoromethylphosphonate (932) at room temperature[778], A one-electron transfer-initiated radical mechanism has been proposed for the addition reaction. Addition to alkynes affords 1-perfluoro-alkyl-2-iodoalkenes (933)[779—781 ]. The fluorine-containing oxirane 934 is obtained by the reaction of allyl alcohol[782]. Under a CO atmosphere, the carbocarbonylation of the alkenol 935 and the alkynol 937 takes place with perfluoroalkyl iodides to give the fluorine-containing lactones 936 and 938[783],... 

Another approach in the study of the mechanism and synthetic applications of bromination of alkenes and alkynes involves the use of crystalline bromine-amine complexes such as pyridine hydrobromide perbromide (PyHBts), pyridine dibromide (PyBn), and tetrabutylammonium tribromide (BiMNBn) which show stereochemical differences and improved selectivities for addition to alkenes and alkynes compared to Bn itself.81 The improved selectivity of bromination by PyHBn forms the basis for a synthetically useful procedure for selective monoprotection of the higher alkylated double bond in dienes by bromination (Scheme 42).80 The less-alkylated double bonds in dienes can be selectively monoprotected by tetrabromination followed by monodeprotection at the higher alkylated double bond by controlled-potential electrolysis (the reduction potential of vicinal dibromides is shifted to more anodic values with increasing alkylation Scheme 42).80 The question of which diastereotopic face in chiral allylic alcohols reacts with bromine has been probed by Midland and Halterman as part of a stereoselective synthesis of bromo epoxides (Scheme 43).82... 

It has recently been reported495 that the complex CsH5V(CO)4 (CSHS = cy-clopentadienyl) is an efficient catalyst for the stereoselective oxidation of cyclohexene to ris-l,2-epoxycyclohexane-3-ol in good yield (65% at 10% conversion). This high stereoselectivity is reminiscent of the highly selective vanadium-catalyzed epoxidations of allylic alcohols with alkyl hydroperoxides discussed earlier. The mechanism of reaction,... 

As models for the investigation of the S i and S i mechanisms the thermal decompositions of alkyl chlorosulfites and allyl chlorosulfites have received considerably more attention than that of other desulfonylation reactions. The usual method of converting alcohols into alkyl chlorides is by treatment with thionyl chloride. This reaction has been shown to proceed through an alkyl chlorosulfite which can often be isolated and shown to decompose by a homogeneous first-order process yielding alkyl chloride and 802 " , although frequently substantial amounts of alkene are formed in the reaction , viz. 

We have further examined the reactions of thiolato-bridged diruthenium complexes with other unsaturated organic substrates. When the cationic Ru complex 4 is treated with cinnamyl alcohol in p-xylene, the allylated aromatic compound 18 is obtained in good yield (Equation 6). We assume a Tc-allyl intermediate because the reaction using l-phenylprop-2-en-l-ol gives, instead of cinnamyl alcohol, the same product 18 however, the detailed reaction mechanism is still obscure. This novel allylation reaction is halogen-free, and may replace the conventional Friedel-Crafts alkylation. 

With the possible exception of hydridocobalamin [42], olefins must be suitably activated with electron-withdrawing substituents to undergo these reactions. Hence, acrylonitrile (X = CN ) and methylacrylate (X = COOCH3) are active alkylating agents [51] but allyl alcohol (X = CH2OH) is not [52]. The mechanism of these reactions is not as well studied, but Schrauzer et al. [53] have presented spectral evidence that the alkylation of cobalt(I) nucleophiles with activated olefins proceeds via a IT complex intermediate (Eqns. 10 and 11). 

The reaction of alkenyl epoxides with organometallic species (lithium, magnesium, copper, and boron) affords allylic alcohols, following an Sn and/or Sn mechanism. These processes can accommodate only little organic functionality and exhibit low regio- and/or stereoselectivity. Under smooth conditions, C—C bond formation proceeds by nucleophilic alkylation of vinyl epoxides in the presence of catalytic amounts of zerovalent palladium. Regio- and stereoselectivity can be achieved via the formation of a Tr-allylpal-ladium complex. Trost and Molander and Tsuji and co-workers simultaneously reported the first studies in 1981. Since then, numerous papers have dealt with this subject. Essentially, after chelation and oxidative addition of the palladium onto the vinyl epoxide, the zwitterionic 7r-allylpalladium complex deprotonates the nucleophile, which can in principle attack either carbon 2 (proximal attack) or 4 (distal attack) (Scheme 1). 

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