Stereoselective [1,2]-Phospha-Brook Rearrangement of CAMDOL-Derived H-Phosphonate: Synthesis of α-Trifluoromethyl...

The Claisen rearrangement is a [3,3] sigmatropic rearrangement of allyl vinyl ethers to unsaturated carbonyl compounds. The rearrangement is a concerted pericyclic reaction proceeding via a chair-like transition state.

In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.

α-Halogenation of aldehydes and ketones is a reaction involving the substitution of α hydrogens with halogens in the presence of a base.  The reaction begins with the abstraction of  α hydrogen by the base to produce a nucleophilic enolate ion. This intermediate undergoes a subsequent nucleophilic substitution with the halogen to produce a monohalogenated carbonyl compound. If the starting substrate has more than one α hydrogen, it is difficult to stop the reaction...

If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...

The method to achieve α-brominated carboxylic acids using a mixture of phosphorus tribromide and bromine is known as the Hell–Volhard–Zelinski reaction. The reaction is catalyzed by phosphorus tribromide, which can be used directly or produced in situ from red phosphorus and bromine. The mechanism comprises PBr3 catalyzed conversion of acid to acid bromide and hydrogen bromide. The acid bromide enolizes to its enol form in the presence of HBr. The nucleophilic enol attacks the...

A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...