Chlorovinyl ketones, enolization

The lack of favorable overlap with the carbonyl t-system makes the a-vinyl deprotonation challenging. However, once a non-planar conformation is enforced, the situation changes dramatically. This is illustrated by facile a-vinyl enoUzation of (E)-p-chlorovinyl ketones by abase as weak as EtjN. The mild a-vinyl enoUzation of these compounds was suggested to originate from their non-planar conformation which, unlike the planar conformation of respective (Z)-isomers, leads to a good orbital overlap between the carbonyl rt-system and the a-C-H bond. The enolization to aUenol is preferred over the a-C(sp )-H bond deprotonation from R. 

Kim, H. Y, Li, J-Y, Oh, K. (2013). A Soft Vinyl Enolization Approach to a-Acylvinyl Anions Direct Aldol/Aldol Condensation Reactions of (E)-P-Chlorovinyl Ketones. Angewandte Chemie International Edition, 52, 3736-3740. 

Chlorovinyl ketones (469) have been shown to undergo lithium(I)-catalysed enolization with EtjN to generate electrophilic lithium [3]cumulenolates (470), which react with nucleophiles, such as another molecule of (469), to stereoselectively produce vinyl allenones (471). °... 

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). 

A very interesting synthetic method of bicyclo[n.l.O]alkanes from cychc ketones via this 1,3-C,H insertion of magnesium carbenoid as a key reaction was reported (equation 22) . 1-Chlorovinyl p-tolyl sulfoxide (76) was synthesized from cyclopentadecanone and chloromethyl p-tolyl sulfoxide in three steps in high overall yield. Lithium enolate of tert-butyl acetate was added to 76 to give the adduct 77 in quantitative yield. a-Chlorosulfoxide (77) in a toluene solution was treated with i-PrMgCl in ether at —78 °C and the reaction mixture was slowly warmed to 0°C to afford the bicyclo[13.1.0]hexadecane derivative 79 in 96% yield through the reaction of the intermediate magnesium carbenoid 78. 

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