Solvometallation

Compound 43 was shown to quantitatively isomerize to the more stable isomer 44. Similar results were obtained when the reaction was carried out with preformed (A1C12)2- The treatment of cyclohexene with a reagent prepared from AlBr3 and potassium gave a product that on D20 quench gave a 11% yield of [1,2-2H2]-cyclohexane indicative of the formation of bis(dihaloaluminio)cyclohexane 483 

Certain metal salts can react with unsaturated compounds with the concomitant addition of a solvent molecule or other nucleophile to yield p-substituted metal derivatives. These reactions, called solvometallations or oxymetallations, have a number of applications in organic synthesis. A short treatment of certain classic and important reactions is given here. 

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Oxythallation is another important solvometallation process.502 The intermediate organothallium compounds formed during addition, however, are seldom isolable, and tend to undergo spontaneous rapid decomposition to form oxidation products. Some examples are discussed in Sections 9.3 and 9.4.1. 

Epoxidation cf vinylallenes 6.3.632 Epoxidation cf vinyl allenic alcohols 6.3333 Solvometallation of vir lallenes 63.63.4 Solvolysis crfalkoxyallenyl alcohols... 

Epoxidation vinyl allenic alcohols 6.3.633 Solvometallation of vinylallenes... 

A similar electrophilic activation of the vinylallene to 2-cyclopentenone cyclization is possible using either mercury(II) acetate or thallium acetate. Solvometallation of allenes is a well studied pro-cess following expected Markovnikov attack at the central carbon by the metal salt. The yield of cyclopentenones was generally higher with acetoxymercuration (49-79%) compared to acetoxythallation (25-68%). Compounds of similar substitution pattern as were investigated with epoxidation (Scheme 31) were prepared. Mechanistically the reaction is remarkable for the facility of solvodemercuration (Scheme 33). Intermediates such as (69) or (70) lose elemental mercury spontaneously in the acetic acid medium to give the 2-cyclopentenones. 

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