Indium‐catalyzed reductive coupling of aromatic carbonyl compounds and imines in the presence of aluminum and chlorosilanes

Abstract

Reductive homocoupling of aromatic aldehydes, ketones, and imines has been achieved in tetrahydrofuran (THF) at room temperature using a catalytic amount of InCl 3 (0.5-3.0 mol %) under a nitrogen atmosphere in the presence of chlorotrimethylsilane (TMSCl) and aluminum metal (Al) to provide the corresponding 1,2-diols and 1,2-diamines, respectively, in good to moderate yields. Other indium compounds such as In(NO 3 ) 3 , cyclopentadienylindium, and indium metal have also been revealed to be effective as catalysts. The catalytic effect of the indium compound is remarkable, and, thus, without it, no reaction occurs in the case of aromatic aldehydes and aldimines, and an induction period is quite long in the case of aromatic ketones. Without either TMSCl or Al, no reaction proceeds even in the presence of the catalyst. Unfortunately, the diastereoselectivity of the products (dl and meso) is not high. Although the precise reaction scheme is not yet clear, we tentatively propose that a redox-active In-Al alloy might be formed on the surface of aluminum in the presence of TMSCl, and an electron transfer from the alloy to substrate might White solid; 1 H NMR [CDCl 3 ‫ם‬ D 2 O (few drops), 400 MHz] d ‫ס‬ 1.64 [1.81] (6H, s), 6.17-7.56 (20H, m); 13 C NMR [CDCl 3 ‫ם‬ D 2 O (few drops), 75.5 MHz] d ‫ס‬

Diastereospecific Coupling of Imines by Low‐Valent Titanium: An Experimental and Computational Study

“…The formation of 2a was confirmed by analyzing the 1 H, 13 C NMR (both 1 H‐coupled and 1 H‐decoupled), and HRMS data. The NMR spectroscopic data of compound 2a was also compared with reported values (Figure S1 in the Supporting Information) 4b,6d. Interestingly, the C–C coupling reaction was found to be diastereospecific, and only the (±)‐isomer was obtained.…”

“…All reactions lead to exclusive formation of the (±)‐isomer. Normally, the benzylic carbon of a (±)‐isomer appears around δ = 63–65 ppm in the 13 C NMR spectra, whereas the corresponding carbon for a meso isomer appears around δ = 60–61 ppm 4b,6d. For all the coupled products, a single benzylic carbon was observed in the 13 C NMR spectra at around δ = 64–65 ppm, which is indicative of the presence of the (±)‐isomer.…”

Some past achievements and future perspectives in main group chemistry

“…Another interesting development is the indium(I) chloride mediated coupling of epoxides with allyl bromide catalyzed by a reusable mesoporous silica-supported palladium catalyst to give homoallyl alcohols [64]. Also, the reductive homocoupling of aromatic aldehydes, ketones and imines to the corresponding 1,2-diols and 1,2-diamines has been reported by the use of a catalytic amount of [In(g 5 -C 5 H 5 )] in the presence of Me 3 SiCl and metallic aluminum [65].…”

Recent Developments in Indium Metal and Its Salts in Organic Synthesis

“…[52] Here, cis-alkenylsilanes give cis products and trans-alkenylsilanes give trans products. These indium(III) halides can also catalyze homocoupling reactions of various aromatic aldehydes, ketones, and imines [53] (Scheme 12).…”