Ketones ring size effects

A similar conclusion has been reached from ring-size effects on rates of base-catalysed (NEt3 in DMF/D20) ionisation of phenyl cycloalkyl ketones [38] for which Shechter et al., (1962) found that the methine proton reactivities have the following relative values (isobutyrophenone chosen as a reference) ... 

Partial rate constants for H-D exchange at the methyl and methine sites of cycloalkyl methyl ketones have been measured chiefly in order to examine the ring-size effect on exocyclic enol and enolate formation. Under base-catalysed... 

The effect of substituents and ring size on this photochemical rearrangement was studied by Paquette and Meehan.(43) Irradiation of the following ketones resulted in steady state mixtures of starting ketone and photoketone whose ratios depended upon structure ... 

It may be of interest to compare the photochemistry of the unsubstituted cyclic ketones. The effect of ring size on the ultraviolet absorption spectrum has been discussed (4,22) although its pertinence to the photochemistry is not obvious. 

An effect of the ring-size in addition to that observed in the elimination taking place in the reduction of vicinal dibromides, has been observed for medium-sized ring compounds which carry the electro-active group either in the side-chain or directly attached to the ring. The half-wave potentials of cycloalkyl bromides can be correlated with the half-wave potentials of cyclic ketones and their derivatives (Fig. 29). The observed relation indicates that the relative effect of ring-size on the reactivity is similar in all the reaction series compared. 

A synthesis of [3]-fused furans involving a ring enlargement can be effected by the treatment of a-alkynyl-a-cyclopropylcycloalkanones with an electron-rich Au(l) catalyst in the presence of a suitable nucleophile (Equation 18) <2006AGE6704>. The nucleophiles that can be used include alcohols, phenols, carboxylic acids, indole, and 2-pyrrolidone. Open-chain ketones as well as other ring sizes react with comparable yields. Silver and lanthanide triflates are also effective catalysts for this transformation. 

The difference between the photoreactivities of cyclobutanone and cyclohexanone has been discussed using Salem theoretical diagrams for coplanar a-cleavage in each ketone. Kimura and co-workers " have studied the effect of ring size on the photochemical reactions of a series of dispiro-cyclobutane-l,3-diones and the derived cyclohexylimines. Funke and co-workers have photolysed a series of cycloalkane carboxaldehydes including cyclobutane carboxaldehyde. 

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