Organoselenium reagents have found varied applications throughout organic chemistry. Like many transition metals selenium can occupy a variety of oxidation states, giving access to a range of redox processes. It may also be bound covalently to organic frameworks that offer the possibility of straightforward catalyst design and tuning for enantio- and stereoselectivity. Hence selenium offers access to a unique niche of reactivity, however, the use of organoselenium compounds as catalysts, or to perform enantioselective transformations, is still an under-exploited area.
The work described herein presents investigations towards the syntheses of chiral organic selenides and diselenides and their applications to enantioselective processes. Catalyst design was centred around cyclic C2-symmetric organic frameworks such as binaphthalene, 2,5-disubstituted tetrahydroselenophenes, dihydroselenepines and dihydroselenocines.
The effectiveness of these reagents in a variety of catalytic processes was tested. Transformations included oxidative processes such as allylic and propargylic C–H oxidation to afford α,β-unsaturated alcohols; Lewis base catalysed halolactonisations; Corey-Chaykovsky epoxidations; and conjugate reactions of alkenylselenonium(IV) species.
During the course of these investigations novel conditions for a palladium-catalysed cross-coupling of aryl electrophiles and organic selenolates were developed enabling the facile synthesis of asymmetric diaryl- and arylalkyl- selenides. The dealkylation of arylalkylselenides was further investigated to enable an alternative route to diselenides.