Ketones cyclic 2-alkoxycarbonyl

Other functional groups which have a heteroatom rather than a hydroxyl group capable of directing the hydrogenation include alkoxyl, alkoxycarbonyl, carboxylate, amide, carbamate, and sulfoxide. The alkoxy unit efficiently coordinates to cationic iridium or rhodium complexes, and high diastereoselectivity is induced in the reactions of cyclic substrates (Table 21.3, entries 11-13) [25, 28]. An acetal affords much lower selectivity than the corresponding unsaturated ketone (Table 21.3, entries 14 and 15) [25]. 

Ketones can be oxidatively carbonylated at the a-carbon via enol intermediates using PdCl2 as the catalyst and Q1CI2 as oxidant [122], The initially formed carbonylation products correspond to a-chlorination and a-alkoxycarbonylation. Under the reaction conditions, these compounds undergo further transformations involving C - C cleavage eventually leading to a mixture of esters and an alkyl chloride or (in the case of cyclic ketones) to a diester and a chloroester (Schemes 20-21). 

The Dieckmann, Thorpe and Thorpe-Ziegler reactions all involve intramolecular cyclization of a stabilized anion to form a cyclic ketone. The Dieckmann reaction is the intramolecular equivalent of the Claisen condensation and yields cyclic 2-alkoxycarbonyl ketones as primary products, whereas the primary products of the Thorpe reaction are 2-cyanoenamines (Scheme 13). Sub quent hydrolysis affords cyclic ketones but the primary products, particularly those from the Dieckmann reaction, have a useful synthetic role (see Section 3.6.3.S.1). 

The reversibility of the process means that cyclic 2-alkoxycarbonyl ketones can be cleaved by alkoxide in the retro-Dieckmann reaction, a process of synthetic significance (see Section 3.6.9.1). More recently, nonequilibrium conditions have been employed in the reaction and this may lead to a change in regioselectivity (see Section 3.6.3.3.3). 

Cyclic ketones bearing an a-alkoxycarbonyl group are reduced by baker s yeast to the (15,2/ )-cycloalkanols often with higher enantio- and diastereoselectivities than those observed with 2-substituted acyclic ketones (vide supra)144,, 45. 

A 1968 patent report has been developed into a practical synthesis of /S-keto-esters by Lewis acid-catalysed condensations of alkyl nitriles with acetoacetates and subsequent acid hydrolysis (Scheme 34). " A new three-step procedure for the alkoxycarbonylation of cyclic ketones consists of an addition of... 

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