Hydration of Unsymmetrical Internal Alkynes: Factors Governing the Regioselectivity

Abstract

Water addition on an unsymmetrical internal alkyne has significance in organic chemistry and has stimulated challenging approaches to access a highly regioselective process. Hydration or formal hydration is presented according to the type of internal alkyne. Methods for electron-rich and -poor diarylalkynes followed by those adapted to arylalkylalkynes are presented. Regioselective hydration reactions of unsymmetrical propargylic and homopropargylic derivatives are then discussed, followed by regioselective aspects of the hydration of internal alkynes directed by carbonyl groups. The following section examines the hydration alkynes linked to CF 3 , esters, ketones, and heteroatoms as haloalkynes, alkynylphosphonates, ynamides, and others. At the end of this section, we report some recent examples of hydration reactions where the alkyne triple bond is connected to an electron-withdrawing group as an ester or a ketone. Reactions are presented, discussed, and illustrated in each of these items through various representative examples. The mechanistic hypotheses explaining the origin of the regioselectivity in the hydration reactions are discussed. This review of recent advances in the regioselective hydration of internal unsymmetrical alkynes (from 2007 until the present) aims to update the current body of knowledge and aid researchers working in this field.

Multicomponent, Multicavity Metallacages That Contain Different Binding Sites for Allosteric Recognition

“…The two ester groups activate the central two alkyne groups, which undergo a selective protonation on the alkyne carbon atoms near the ester groups. The addition of H 2 O on the resulting carbocation leads to an enol that tautomerizes into ketone to form ligand 1 . However, because the two side alkynes are far from the ester groups, it is difficult for them to undergo hydration by H 2 O.…”