Isolable and Readily Handled Halophosphonium Pre-reagents for Hydro- and Deuteriohalogenation

Although
the addition of acid halides across olefins is well-studied,
limitations remain with a number of substrate classes that possess
leaving groups, polyunsaturation, and acid-sensitive moieties, particularly
polyenes prone to cyclization. The process is also challenging when
conducted on a small scale, and moreover, methods for the addition
of their deuterated counterparts typically require special techniques,
especially when control of stoichiometry is required. Herein is described
a readily synthesized and handled reagent class which can accomplish
the controlled and selective Markovnikov addition of both HCl and
HBr across several alkene classes under mild reaction conditions tolerant
of diverse functionality. The process is particularly valuable on
a laboratory scale, and direct comparisons to other methods are provided.
As a result of in-depth mechanistic studies seeking to understand
how these novel tools work and the active species behind their efficacy,
the means to easily add DCl and DBr using a controlled amount of D2O was discovered along with the critical role of hydrolysis
in leading to active hydrohalogenation species.