[3652-92-4] · C15H16N2 · 1,3-Dimethyl-2-phenylbenzimidazoline · (MW 224.33)
(heterocycle capable of reducing a-halo ketones, a,b-unsaturated carbonyl compounds, and a-nitro sulfones)
Alternate Name: DMBI.
Physical Data: mp 94 °C.
Preparative Method: N1,N2-dimethyl-o-phenylenediamine is condensed with benzaldehyde in methanol-acetic acid. The product is purified by recrystallization from petroleum ether.1 The spent reagent may be recovered and reactivated by Sodium Borohydride in methanol.5
DMBI has been found to dehalogenate a-halo ketones and halogenated benzophenones without affecting the carbonyl group (eq 1) (see also Tri-n-butylstannane). The mechanism was identified as a radical chain process containing a SET-hydrogen atom abstraction/propagation sequence.2 The reaction typically requires initiation, e.g. by Azobisisobutyronitrile (AIBN) or Di-t-butyl Peroxyoxalate (DBPO). Thiophenol may be used to catalyze the transformation, for sluggish tertiary halo ketones, by facilitating the hydrogen atom transfer step.3
DMBI was reported to reduce a,b-unsaturated ketones to the corresponding saturated ketones in the presence of a Lewis acid (eq 2). Aluminum Chloride was found to be the acid of choice, with stoichiometric quantities being required.4 The reaction failed for a,b-unsaturated aldehydes and in the absence of a Lewis acid.
a-Nitro sulfones were desulfurized when exposed to DMBI (eq 3).5 The mechanism was found to be a radical chain process which typically requires initiation. More well-known desulfurization reagents, such as Raney Nickel or catalytic hydrogenation, would not be expected to leave the nitro group intact. DMBI was also superior to N-benzyl-1,4-dihydronicotinamide for this transformation.
DMBI is conveniently prepared from available starting materials. The reagent may be recovered and recycled. The reagent is most often used in mechanistic studies. No preparative (i.e. 0.1 mol) uses are available in the current literature.
Great Lakes Chemical Corporation, West Lafayette, IN, USA