1.1- dimethylcyclohexane-type intermediate

When an a-chloroaldehyde or an a-chloroketone is condensed with a /3-ketoester, in the presence of aqueous base, a furan is produced bearing an ester substituent at the /3-position. It is thought that the reaction is of the aldol type intermediate dihydrofurans (256) have been isolated in certain cases (Scheme 70) (74BSF519). The condensation of ethyl bromopyru-vate and sodium oxaloacetate follows a similar mechanism (54JOC1671). The one-pot synthesis of 2,4,5-trisubstituted furans (257) from ketones and ethyl 3,4-dibromo-2-butenoate is a useful addition to a well known route (80S52). The analogous reaction of cyclic /3-diketones, i.e. cyclohexane-1,3-dione and 5,5-dimethylcyclohexane-l,3-dione, results in the formation of the condensed furans (258) and (259). These reactions are preformed either in ethanol with sodium ethoxide or in DMF with potassium carbonate. 

Steric effects affecting the mode of adsorption as well as the type of intermediates formed on different metals are decisive factors in determining product distributions. 1,3-Dimethylcyclohexene and 1,5-dimethylcyclohexene yield an identical mixture of cis- and trims-1,3-dimethylcyclohexane on palladium 63... 

The radical mechanism is further supported by several other results in which stereochemical scrambling and isotope scrambling are observed in the sMMO-catalyzed hydroxylation of hydrocarbons. Retention of stereochemistry is a valid measure of the concertedness of a reaction only if it can be assumed that the retention is not due to constrains imposed by the active site geometry of the enzyme. Loss of stereochemistry is absolutely indicative of a reaction requiring an intermediate and thus implies a nonconcerted reaction [2]. Scrambling of stereochemistry was observed with hydroxylation of c/5-l,4-dimethylcyclohexane and c/ -l,3-dimethylcyclohexane with sMMO system from Af. capsulatus (Bath) as shown in eqs. (7) and (8) [75]. This type of stereochemical scrambling was also observed in the hydroxylation of norbornane by rabbit liver microsomes and in the oxidation of camphor by cytochrome P-450 [2]. 

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