The Johnson-Claisen (also known as the ortho ester Claisen rearrangement) uses catalytic acid and heat to produce a γ,δ-unsaturated ester from an allylic alcohol and excess trialkyl orthoacetate. One of the alkoxy groups of the orthoacetate is first exchanged for the allylic alcohol, followed by an internal proton transfer from...

N-chlorosuccinimide (NCS), dimethylsulfide (DMS) and triethylamine (TEA) are used to efficiently convert 1° or 2° alcohols into aldehydes and ketones respectively. First, NCS and DMS react to form the Corey-Kim reagent or S,S-dimethylsuccinimidosulfonium chloride, via dimethylsulfonium chloride. The nucleophilic 1° or 2° alcohol then attacks the Corey-Kim reagent, resulting in...

The thermal [3,3]-sigmatropic rearrangement of 1,5-dienes to the isomeric form is known as the Cope rearrangement, which can only be detected when the 1,5-diene substrate is substituted. As a reversible reaction, the forward direction is favored when the product is stabilized by conjugation or the resulting double bond is more...

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...