Allenyl enolates formation

DFT study of interception of the allenyl enolate intermediate of Meyer-Schuster rearrangement using aldehydes and imines has shown that the active form of the vanadium catalyst bears two triphenyl siloxy ligands and that vanadium enolate is directly involved in the C-C bond formation." DFT calculations have elucidated the mechanisms and diastereoselectivities of phosphine-catalysed [4-1-2] annulations between allenoates and ketones or aldimines (Scheme 44). 

The transient allenyl enolate intermediate of the vanadium-catalysed Meyer-Schuster rearrangement with aldehydes and imines has been studied computationally and the active form of the catalyst is considered to contain two triphenylsiloxy ligands. The transesterification of vanadate occurs via tr-bond metathesis and the vanadium enolate is directly involved in the key C-C bond formation (Scheme 175). ... 

A new type of triaryl phosphine-functionalized imidazolium salt containing cations such as (6) has been prepared. Palladium complexes of (6) generated in situ have been used successfully in Heck-type reactions of aryl halides with acrylates and of 4-bromotoluene with styrene derivatives.34 The first Heck-type reaction of aryl halides with allenes has been reported. 1,3-Double arylations were observed with 3-substituted-l,2-allenyl sulfones, while 1-monoarylation was favoured with 3,3-disubstituted-l,2-allenyl sulfones.35 It has been shown that the a-arylation of methane-sulfonamides (7) may be achieved using palladium catalysis reaction proceeds through the sulfonamide enolates.36 It is also reported that palladium cross-coupling of alkynes with /V - (3 - i odophe n y I an i I i ncs) may lead to the formation of substituted carbazoles.37... 

By analogy with the mechanistic pathway described for the enol ether 119 (Scheme 44), we believe that the transformation of 123a-c also occurs via the formation of the /J-metalated allenyl intermediate, generated from the -elimination of the corresponding zirconacyclopropane and subsequent rearrange-... 

DienonesJ A new synthesis of 2,4-dienones (4) involves reaction of an allylic alcohol (1) with an allenyl phenyl sulfoxide (2) in benzene (ice bath). The resulting enol ether (3) is treated with this base, which induces Claisen rearrangement and elimination of benzenesulfenic acid, with formation of the dienone 4 (equation I). 

Zard has studied the isomerization/Mislow-Evans rearrangement of vinyl sulfoxides such as 237, arising from enolate addition to alkynyl sulfoxides [Scheme 18.60). Isomerization of 237 to the allylic sulfoxide 238 enabled the [2,3]-sigmatropic rearrangement to a-hydroxy-a-vinyl ketone 239. In this case, diastereoselectivity was low in formation of the carbinol center within a steroid framework. Additions to allenyl sulfoxides provide a similar sequence, leading to 2-propenyl substitution at the tertiary alcohol center (not shown). 

The elimination pathway of stereochemically defined / -halovinyl ketones has been investigated using triethylamine leading to the formation of allenyl ketones and propargyl ketones. A preferential a-vinyl enolization of ( )- -chlorovinyl ketones has been observed where a nonplanar s-cis conformation is proposed as a dominant conformation as opposed to a planar s-cis conformation of (Z)- -chlorovinyl ketones. The synthetic utility of the elimination reaction of j5-chlorovinyl ketones was further demonstrated for a one-pot synthesis of 2,5-disubstituted ftirans in the presence of 1 mol % CuCl (Scheme 2). 

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