Selective radical reactions in multiphase systems: phase-transfer halogenations of alkanes.
PMID 11775673 · Chemistry (Weinheim an der Bergstrasse, Germany) · 2001 · DOI 10.1002/1521-3765(20011203)7:23<4996::aid-chem4996>3.0.co;2-p
Authors: P R Schreiner; O Lauenstein; E D Butova; P A Gunchenko; I V Kolomitsin; A Wittkopp; G Feder; A A Fokin
Abstract
The present paper shows that selective radical reactions can be initiated and carried out in multiphase systems. This concept is applied to the selective functionalization of unactivated aliphatic hydrocarbons, which may be linear, branched, and (poly)cyclic, strained as well as unstrained. The phase-transfer system avoids overfunctionalization of the products and simplifies the workup; the selectivities are excellent and the yields are good. This is the only method for direct preparative iodination of alkanes applicable to large scale as well. We demonstrate that the reaction systems are indeed phase-transfer catalyzed through a systematic study of variations of the reactants, solvents, catalysts, and by measuring as well as computing the H/D kinetic isotope effects for the rate-limiting C-H abstraction step by *CHal3 radicals which are held responsible for the observed radical reactions. In the case of *CBr3, this key intermediate could also be trapped under otherwise very similar reaction conditions. To stimulate further work, the tolerance of some functional groups was tested as well.
Cite
P R Schreiner; O Lauenstein; E D Butova; P A Gunchenko; I V Kolomitsin; A Wittkopp; G Feder; A A Fokin. Selective radical reactions in multiphase systems: phase-transfer halogenations of alkanes. Chemistry (Weinheim an der Bergstrasse, Germany) (2001). PMID 11775673. DOI 10.1002/1521-3765(20011203)7:23<4996::aid-chem4996>3.0.co;2-p.