Radical Coupling of Iodocarbonyl Compounds with Butenylindium Generated by Transmetalation between Cyclopropylmethylstannane and Indium Halides

Abstract

The reaction of cyclopropylmethylstannane 1 with R-iodocarbonyl compounds 2 in the presence of either InBr 3 or InCl 3 gave the C-C coupling products 3. Various types of iodocarbonyl compounds such as esters, amides, and ketones were applied to this system to afford the corresponding cyclopropylethylsubstituted carbonyls 3. Transmetalation between cyclopropylmethylstannane and indium halides afforded butenylindium dihalide and dibutenylindium halide, as confirmed by NMR spectroscopy. The reactivity of dibutenylindium halide was greater than that of monobutenyl species. The active species, dibutenylindium halide, was stabilized by complexation using DPPE, and its structure was analyzed using X-ray crystallography. The solid state of the complex shows a linear structure with a core (-Cl-In-Cl-In-P-C-C-P-In-) n with five-coordinated indium centers. The reaction between 1 and 2, mediated by indium halides, proceeded in a radical manner. The in situ-generated alkylindium species and a small amount of oxygen, which can be supplied by atmospheric air, initiated the radical reaction.

Synthesis of Cyclopropane‐Containing Phosphorus Compounds by Radical Coupling of Butenylindium with Iodo Phosphorus Compounds

“…First, we examined the coupling reaction using InBr 3 in toluene at room temperature. Although these conditions are considered optimal for radical coupling with α-iodo carbonyl compounds, [8] the reaction yield was low (Entry 1). Raising of the reaction temperature improved the yield to 48 % (Entry 2).…”

“…The additives examined in Table 1 were also purchased from commercial sources. (Cyclopropylmethyl)stannane 1 [8,14] was prepared according to a known method, and this compound is reported. Iodo phosphorus compounds 2b, [27] 2e, [6b] 2g, [6b] and 5 [6b] were prepared according to known methods, and these compounds are reported.…”

“…All other reagents are commercially available. [8] To a flask containing magnesium (230 mmol) in THF (150 mL) was added Bu 3 SnCl (200 mmol). The mixture was cooled to 0°C, and allyl chloride (230 mmol) was added.…”

“…Recently, we found that a butenylindium species generated from the transmetalation between a (cyclopropylmethyl)stannane [7] and an indium halide was a useful reagent for radical coupling with α-iodocarbonyl compounds to afford cyclopropylmethylated carbonyl compounds. [8] Herein, we report the unprecedented radical coupling of the butenylindium species with iodo phosphorus inert to the reaction system. In addition, the transmetalation of a (cyclopropylmethyl)stannane and InBr 3 provided the dibutenylindium bromide as a single product, which smoothly coupled with the unstable phosphonyl radical species from the iodo phosphorus compound.…”

Isolation and Crystallographic Characterization of Allylindium Species Generated from Allyl Halide and Indium(0)

“…To stabilize and isolate the species, pyridine was added to the mixture as a coordinative ligand (1/In = 1:1). [5,6,10] The 1 H NMR spectrum showed that both species 2 and 3 were complexed by the ligand (see Supporting Information), but a solid was not obtained after the usual treatment. Next, the addition of 3,5-dibromopyridine (Br 2 py) gave complexed species of 2 and 3 at an integration ratio of 1:1.38 (= 2·L n /3·L n ) (Chart c).…”