Indium(III) Chloride−Sodium Borohydride System:  A Convenient Radical Reagent for an Alternative to Tributyltin Hydride System

Abstract

The indium hydride generated from NaBH4 and InCl3, is a promising candidate of alternative to Bu3SnH. In particular, the catalytic performance of InCl3 in the dehalogenation of alkyl and aryl halides, intramolecular cyclization and intermolecular coupling reaction are noteworthy.

Synthesis of dichloroindium hydride and exploration of its reactivity with organic functional groups. Tandem, selective and partial reductions of halo-nitriles

“…However, the same reaction is low yielding in THF (only 15% reduction) under otherwise similar reaction conditions (Table 3, entry 5). 23 Similar solvent effects were observed by others working with HInCl 2 .…”

“…32 Consequently, we reacted a 1:1 molar ratio of InCl 3 to NaBH 4 in both THF and MeCN and analyzed the supernatant solution by 11 B NMR spectroscopy to probe the identity of the boron species formed in situ (Scheme 27). We suggest that the poor reduction of alkyl halides using a catalytic amount of InCl 3 along with one equivalent of NaBH 4 in THF that was previously reported 23 is likely to have been due to the inhibition of the catalytic cycle by the in situ generated BH 3 ·THF. Consequently, when a stoichiometric amount of InCl 3 was used along with three equivalents of NaBH 4 , (3-bromopropyl)benzene was fully reduced to n-propylbenzene with an isolated yield of 80%, indicating that BH 3 ·THF or the solvent THF has little effect on stoichiometric reductions involving HInCl 2 .…”

“…Intramolecular cyclization of 1-allyloxy-2-iodobenzene. 23 Representative InCl 3 /NaBH 4 intermolecular radical additions were also demonstrated using iodobenzene and electron-deficient olefins (Scheme 22).…”

“…Radical addition of iodobenzene to electron-deficient olefins. 23 In subsequent work, Ranu and coworkers used the InCl 3/ NaBH 4 system to generate HInCl 2 and chemoselectively reduced conjugated alkenes (Scheme 23). 24,25 Scheme 23.…”

“…31 Although a considerable number of studies have examined the InCl 3 /NaBH 4 system, few have reported on the significant influence that solvent can have on reaction rates and yields of reductions. 23,31 For example, Baba and coworkers report that alkyl halides were reduced efficiently (up to 78% reduction) using a catalytic amount of InCl 3 along with one equivalent of NaBH 4 in MeCN (Table 3, entry 4). However, the same reaction is low yielding in THF (only 15% reduction) under otherwise similar reaction conditions (Table 3, entry 5).…”