Allylic derivatives carbonylation, acetate compounds

Another isohypsic transformation of special significance involves elimination of H-X elements from allylic derivatives to form 1,3-dienes. Besides being extremely important compounds as monomers, 1,3-dienes occupy a unique position in synthetic practice as components in the Diels-Alder reaction. One of the common routes of synthesis of 1,3-dienes also employs a vinyl Grignard addition to carbonyl compounds as the initial step (Scheme 2.55). Allylic alcohols thus formed can easily undergo 1,2-elimination (in some cases it is preferable first to transform the alcohols into their respective acetates). 

Dilithium tetrachlorocuprate is recommended as an additive for cross coupling of Grignard compounds with tosylates even allylic and benzylic acetates give good yields . a-Methylene-ketones, -carboxylic acids and -lactones have been prepared via sulfides and sulfoxides. A convenient and general synthesis of acetylene derivatives from boranes via the reaction of iodine with lithium 1-alkynyltriorganoborates has been published ar-Nitrostyrenes can be easily obtained by a Wittig synthesis with formaldehyde in an aqueous medium . A new synthesis of unsym. ketones by reaction of dialkyldiloroboranes with lithium aldimines has recently been published . Metallo aldimines have also served for the synthesis of a variety of other compound classes such as a-hydroxyketones, a-keto acids, nitriles, and for the asym. synthesis of a-amino acids . Polycondensations of malononitriles with benzylic chlorides have been carried out quantitatively under mild conditions in dimethyl sulfoxide with triethylamine as acid acceptor . Carbonyl compounds can react with dibromoacetonitrile to yield a-bromo esters with additional carbon atom . ... 

Halides are the dominating starting materials for carbonylation of aryl-X derivatives. This is not true for benzyl-X and allyl-X compounds. Here, alcohol derivatives [26] such as acetates, carbonates, ethers, and phosphates, and the alcohols themselves, are more important today. According to Murahashi et al. [27] the reactivity of the leaving group of allylic substrates decreases in the order... 

Following from the examples of allyltrichlorosilanes 21.5, Denmark introduced the related eno)g4 richlorosilanes 21.97 (Scheme 21.13) to cany out Mukaiyama-lype nucleophilic additions to carbonyl compounds. " According to Mayr s nucleophilicity scale, silyl enol ethers derived from aldehydes and ketones and, in particular, silyl ketene acetals are even more powerful nucleophilic reagents than the respective allyl silanes. Indeed, the aldol-type addition of trichlorosilyl enol ethers 21.97a-d to aldehydes 21.4 proceeds readily at room temperature without a catalyst exhibiting simple first-order kinetics in each component (Scheme 21.13), which contrasts with the lack of reactivity of allyl silanes in the absence of a catalyst. 

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