The Birch 1,4-reduction of an aromatic ring to its corresponding unconjugated cyclohexadiene, involves an alkali metal dissolved in liquid ammonia in the presence of an alcohol. An electron from the metal interacts with the aromatic ring, resulting in a carbanion and a radical. The carbanion abstracts a proton from the...

The Claisen [3,3]-sigmatropic rearrangement uses either heat or a Lewis acid to convert an allyl vinyl ether to an γ,δ-unsaturated carbonyl compound via an early six-membered chair-like transition state. In acyclic systems, large groups adopt equatorial positions to minimize unfavorable 1,3-diaxial interactions. When a chair-like structure is disfavored, the reaction...

The Clemmensen reduction uses amalgamated zinc (Zn/Hg) and hydrochloric acid to reduce an aldehyde or ketone to an alkane. Two proposed mechanisms exist: the “Carbanionic mechanism” involves zinc directly attacking the carbonyl group and the formation of carbanion intermediates, while the “Carbenoid mechanism” occurs on the surface of zinc, involving...

The thermal decomposition of an acyl azide to an isocyanate and nitrogen gas is known as the Curtius rearrangement. The R group of the acyl azide migrates to its nearest nitrogen, releasing nitrogen gas to form the isocyanate product, which can further react with nucleophiles in solution, i.e. exposure to...

Known also as the "Eschweiler-Clarke methylation", this reaction converts a 1° or 2° amine to a 3° amine in a one-pot reaction with excess aqueous formic acid and formaldehyde. An iminium ion is first formed from the starting amine and formaldehyde via an aminal intermediate. A hydride transfer from the...

The Bartoli indole synthesis uses an alkenyl Grignard reagent in excess at low temperatures and an acid work-up to convert a substituted nitroarene to an indole. The mechanism is not clear in every detail, but the main steps have been elucidated. The first equivalent of the Grignard reagent attacks the...