Reduction and reductive alkylation of cycloheptatriene with alkali metals in liquid ammonia

When treated with alkali metals in liquid ammonia at −70° cycloheptatriene adopts two electrons and a proton yielding the cycloheptadienyl anion. Protonation of this anion yields 1,3‐ and 1,4‐cycloheptadiene in a ratio which depends rather strongly on the proton donor used. Decreasing acid strength of the proton donor favours 1,3‐cycloheptadiene formation. The selectivity of protonation also depends on the alkali metal used and on the concentration. At −33° ammonia protonates the cycloheptadienyl anion yielding 1,3‐cycloheptadiene. This enables one step reduction of cycloheptatriene to cycloheptene. Reduction of 7‐deuterocycloheptatriene shows the first proton addition to cycloheptatriene to be irreversible. Alkylation of the cycloheptadienyl anion yields mixtures of 3‐alkyl‐1,4‐cycloheptadiene and 5‐alkyl‐1,3‐cycloheptadiene in which the former compound invariably predominates.