Coupling, of allyl groups

Cross-Coupling of Allylic Groups with Hard Carbon... 

In view of the synthetic applications, among carbanions stabilized by only one divalent sulfur atom, allylic thiocarbanions proved to be particularly valuable, as shown with Biellmann coupling of allylic groups, applied to an elegant synthesis of squalene from farnesyl bromide [301]. In this synthesis, the retention of the allylic double bond position and stereochemistry in both the metallation-alkylation and the desulfurization steps are noteworthy. However, the results are not always as clear-cut, and... 

Coupling of allyl group to the terminus of another polymer... 

Dienes and allylarcncs can be prepared by the Pd-catalyzcd coupling of allylic compounds with hard carbon nucleophiles derived from alkenyl and aryl compounds of main group metals. Allylic compounds with various leaving groups can be used. Some of them are unreactive with soft nucleophiles, but... 

Organoboranes are reactive compounds for cross-coupling[277]. The synthesis of humulene (83) by the intramolecular cross-coupling of allylic bromide with alkenylborane is an example[278]. The reaction of vinyiborane with vinyl-oxirane (425) affords the homoallylic alcohol 426 by 1,2-addition as main products and the allylic alcohol 427 by 1,4-addition as a minor product[279]. Two phenyl groups in sodium tetraphenylborate (428) are used for the coupling with allylic acetate[280] or allyl chloride[33,28l]. 

Many compounds are now known which contain simple allyl residues bonded sideways to a metal. Table IX is a summary of the proton resonances for the scries. The coupling constants in general are more characteristic than the chemical shifts of allyl groups bonded in this way (139), but the scattered data are not complete enough to permit a summary of this aspect, so far as the nickel family is concerned. 

Coupling of an aryl triflate with an arylstannane is a good mediod for the preparation of biaryls and other bis-aromatic species of all types. Coupling of vinyl groups takes place with retention of stereochemistry. Furdiermore transfer of die allyl group occurs smoothly. 

Apart from halides, pseudohalides and acetates, FeCl3 is able to activate hydroxyl groups in a similar manner. Hence various substitutions of hydroxyl groups have been developed, e.g. the condensation of alcohols or phenols with diphenylmethanol to give DPM-protected alcohols [Equation (7.4), Scheme 7.11] [15] or the direct coupling of allylic or benzylic alcohols with C—H-acidic compounds [Equation (7.5)] [16]. 

Cross-coupling of allylic compounds occurs by transmetallation between 7i-allyl intermediates and organometallic compounds of Mg, Zn, B, Al, Si and Sn, and subsequent reductive elimination. Reaction of the allylic dithioacetal 180 with MeMgBr in the presence of an Ni catalyst affords alkenes 184 bearing a tert-butyl group [90]. In this reaction, generation of the 7i-allylnickel 181 by oxidative addition and subsequent transmetallation with MeMgBr afford 182. Then the methylated product 183 is formed by reductive elimination, and finally the dimethylated product 184 is formed by the sequence of similar reactions. 

Coupling of functional groups onto the walls of mesoporous silica materials can also be achieved by surfactant-templated assembly of an organosilicon alkoxide and silicon alkoxide reagents. Recent reports that use this synthetic strategy include hybrids of methacrylate-mesoporous silica [104], phenyl-amino (thiol or allyl)-mesoporous silica [105], and organic chromo-phore-mesoporous silica [106]. 

Cross-coupling of allyl halides with vinyltin reagents. Allyl halides couple with vinyl- or aryltin reagents in the presence of this catalyst in uniformly high yields (>80%). A wide variety of functional groups is tolerated. The geometry of the double bond in both partners is retained, but the carbon-to-carbon bond is formed with inversion at the allylic position. 

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