3- Alkyl-6-hydroxy-2-cyclohexenones

Alkyl-6-hydroxy-2-cyclohexenones The heterocycle of the Birch reduction (Na,... 

Deprotonadon of thioanisole and addition of a carbonyl compound affords an isolable hydroxy sulfide which can then be alkylated (Scheme 7). Treatment with base generates the same betaine that would have been formed using the sulfur ylide approach, and effects the intramolecular displacement reaction. The addition of methylthiomethyllithium to 2-cyclohexenone exclusively provides the 1,2-addition prod-uct the dianions derived from phenylmethanethiol or allylthiol react in a similar manner. In one case a 6-keto steroidal substrate was found to undergo smooth methylenation using this procedure. 

Procedures which utilize selenides are similar, but a-lithio selenides are not generally preparable via simple deprotonation chemistry, due to facile selenium-lithium exchange. - Selenium-stabilized anions are available, however, by transmetalladon reactions of selenium acetals and add readily to carbonyl compounds. The use of branched selenium-stabilized anions has been shown to result exclusively in 1,2-addidon to unhindered cyclohexenones, in contrast to the analogous sulfur ylides. The resulting 3-hydroxy selenides undergo elimination by treatment with base after activation by alkylation or oxidation (Scheme 10). An alternative method of activating either p-hydroxy selenides or sulfides toward elimination involves treatment of a chloroform solution of the adduct with thallium ethoxide (Scheme 11). A mechanism involving the intermediacy of a selenium ylide is proposed. 

The azadienyllithium reagent derived from the yvjv-dimethylhydrazone of crotonaldehyde when allowed to react with simple ketones yielded a,p-unsaturated-8-hydroxy-N,N-dimethylhydrazone products, resulting from 1,2-addition at the 7-carbon. This is in contrast to alkylation which occurs at the a-carbon (cf. equation 13) and to the reactivity of (42 equation 16) with cyclohexenone which led to mixtures of Michael adducts arising from electrophilic substitution at both the a- and 7-carbons. ... 

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