Electrophilic allyl derivatives

Alkenylbenzotriazoles 865 are readily prepared by isomerization of the corresponding allyl derivatives catalyzed by Bu OK. Lithiated compounds 865 are treated with electrophiles to provide a-substituted derivatives 866. Epoxidation of the double bond with ///-chloroperbenzoic acid converts intermediates 866 into oxiranes 867 that can be hydrolyzed to furnish a-hydroxyketones 868 in good yields (Scheme 140) <1996SC2657>. 

Notice that the final result is a 1,3 charge affinity inversion Umpolung) of an allylic derivative via a FGI of a functional group of type E by a group of type A, followed by a [2,3]-sigmatropic rearrangement. If the intermediate allyl anion reacts with a carbonyl compound as the electrophile the result is then a 1,4-D system, such as ... 

If the ring becomes more strained in the transition state nucleophilic substitution should proceed more slowly than with similar, non-cyclic electrophiles. Thus, cyclopropyl derivatives are highly resistant towards nucleophilic substitution because the RCR angle is fixed at 60°, and only rarely can products of an Sn2 reaction at cyclopropyl derivatives be obtained [109]. Instead, allyl derivatives are usually the main products (Scheme4.23). 

Vinylthiopyridines, e.g. (496) and (497), available by various methods, on acid catalysis can be cyclized to dihydrothiazoles. For allyl derivatives (498) cyclization by acid or electrophilic catalysis yields 3-methyl derivatives (81H(15)1349). 

Attempts to bring about cross coupling of different allylic halides invariably led to mixtures suggesting exchange of the allylic units before coupling. This problem in synthesis is better solved by cross coupling of an allylic halide and an allylic derivative of a main group metal. However, electrophilic alkylation of )) -allyl-NiBr dimers by simple alkyl halides is successfiil (equations 130 and 131). 

Diethyl diazomalonate (142) reacts with allyl bromide in the presence of a Rh catalyst to produce only minor amounts of the cyclopropane 174 together with the ylide derived malonate ester (173) . With allyl chloride the electrophilic cyclopropane derivative 174 is produced predominantly (equation 41). 

PtMeL2] proceed in a Markownikov manner by electrophilic attack of Pf thus [Pt(A -2-methallyl)L2] is formed from allene and [PtMe-(acetone)L2], whereas the analogous 1,3-butadiene cation does not lead to a 7r-allylic derivative by Pt—Me insertion. The hydro cation, however, can react by either a Markownikov or an anti-Markownikov mechanism with either Pt+ or attack on the unsaturated ligand. This apparent versatility leads to the formation of Tr-allylic complexes from both allenes and 1,3-dienes with [PtHLg]. ... 

Just as anions of allyl derivatives can be homoenolate equivalents (chapter 13) so anions of vinyl derivatives can be acyl anion equivalents. Vinyl (or enol) ethers can be lithiated reasonably easily, especially when there is no possibility of forming an allyl derivative, as with the simplest compound 81. The most acidic proton is the one marked and the vinyl-lithium derivative 82 reacts with electrophiles to give the enol ether of the product17 84. However, tertiary butyl lithium is needed and compounds with y-CHs usually end up as the chelated allyl-lithium 85. These vinyl-lithium compounds add directly to conjugated systems but the cuprates will do conjugate addition.18... 

The coupling reactions with the benzoyl chloride and allyl iodide required the addition of 10% Cul as catalyst to yield the corresponding ketone and allyl derivatives. In the absence of copper iodide catalyst, the prementioned two electrophiles gave only low yields ofthe expected products. 1,2-Dibromoethane was used to remove the excess of magnesium when benzoyl chloride or ally iodide was used as electrophiles (entries 6 and 7), and it did not react with the Grignard reagents under the given reaction conditions. 

Grignard substitution on allylbromide gave allyl derivative 3 while chlorodimethylvinylsilane and methylacetate gave olefin intermediates 1-2 via substitution with the aryllithium derivative. Formation of bis-TFVE olefin 2 is illustrative of the pronounced reactivity of TFVE-Li toward organic electrophiles. Addition of methyl acetate to a solution of TFVE-Li, followed by protonation, yields the tertiary alcohol [p-F2C=CFOC6H4]2C(CH3)OH, which undergoes rapid dehydration to afford the bis-TFVE olefin 2. Isolated yields of 1-3 after short path... 

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