Carbonates, allylic, coupling from alcohols

Radical Coupling and Cyclization Reactions. Phenyl thionocarbonate esters derived from alcohols serve as efficient precursors for the generation of radical intermediates which can be used for the formation of new carbon-carbon bonds. For example, a 4-thionocarbonate ester derived from L-lyxose undergoes a stereoselective allylation upon photolysis in toluene in the presence of 2.0 equiv of allyltributylstannane (eq 6). Photochemical initiation is preferable to chemical initiation using azobisisobu-tyronitrile which results in the formation of side products at the... 

Homoallylic alcohol 9 is readily prepared by palladium-catalyzed directed cyanoboration followed by Suzuki-Miyaura cross-coupling (Scheme 5.15) [15]. Palladium-catalyzed allyl transfer from 9 to aryl bromide results in removal of the hydroxymethyl directing group and concomitant formation of 3,4-diaryl-2-butenenitrile albeit the lack of regio- and stereospecificity. The overall transformation proposes a concept of intramolecular reaction with a carbon tether removable through retro-allylation. 

In the synthesis of alkylidenecyclobutenes from propargyl alcohols, stoichiometric experiments show that the first step involves [2+2] oxidative head-to-head coupling of the alkynes, leading to an isolable cyclobutadiene-ruthenium complex. Addition of acid generates a cyclobutenyl metal intermediate which undergoes carboxylate addition on the less substituted allylic carbon atom (Scheme 7). 

Allyl silanes react with epoxides, in the presence of Bp3 OEt2 to give 2-allyl alcohols.The reaction of a-bromo lactones and CH2=CHCH2Si(SiMe3)3 and AIBN leads to the a-allyl lactone.On the other hand, silyl epoxides have been prepared from epoxides via reaction with iec-butyllithium and chlorotri-methylsilane. ° a-Silyl-A-Boc-amines were prepared in a similar manner from the A-Boc-amine. " Arylsilanes were prepared by reaction of an aryl-lithium intermediate with TfOSi(OEt)3. In the presence of BEs etherate, allyl silane and a-methoxy A-Cbz amines were coupled. Benzyl silanes coupled with allyl silanes to give ArCHa—R derivatives in the presence of VO(OEt)Cl2 " and allyltin compounds couple with allyl silanes in the presence of SnCl4. Allyl silanes couple to the a-carbon of amines under photolysis conditions. 

Trost chose to exemplify the utility of organopalladium coupling reactions for carbon-carbon bond formation by use of this process for the ring closure step in a synthesis of 1 (Scheme 1.9) To this end, monoprotected diol 31 was oxidized and chain extended to form the a,p-unsaturated ester 32. Reduction to the allylic alcohol followed by acetylation and desilylation gave 33 in 53% overall yield from 31. Carboxylic acid 35 was then obtained via a two-step sequence from bromo ester 34 (84%) by alkylation with methyl... 

Allylic alcohols react differently. The coupling product has a saturated carbon chain in which the hydroxyl group has been oxidized to a formyl or keto group (7). The yields from 3-bromopyridine were generally high a methyl group on an olefinic carbon in the alcohol retards the reaction (78JOC3396). 

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