Synthesis of Te‐alkyl carbamotelluroates from tellurium, carbon monoxide, amines, and alkyl halides

Abstract

Lithium amides reacted with tellurium under atmospheric pressure of carbon monoxide to yield lithium carbamotelluroates which were trapped with alkyl halides to give Te-alkyl carbamotelluroates in good yields. Results of control experiments suggested that lithium carbamotelluroates were formed by the reaction of tellurium with carbamoyllithiums generated in situ from lithium amides and carbon monoxide. It was revealed also that yields were imprwed when tellurium was preliminarily treated with Iithium amides prior to the introduction of carbon monoxide into the reaction media.Carbamoyllithiums are attractive reagents for nucleophilic introduction of carbamoyl moieties into organic molecules [ 13. Their synthetic utility has been demonstrated clearly by our recent study which achieved efficient generation of carbamoyllithiums from carbamotelluroates by lithium-tellurium exchange reactions and their successful trapping with a variety of electrophiles [lb]. In order to make this transformation practically useful for organic synthesis, general and convenient synthetic methods of carbamotelluroates are strongly demanded. The hitherto known methods for their preparation are limited only to the substitution of . As for the selenium analogues, Se-alkyl carbamoselenoates were obtained in good yields by the alkylation with alkyl halides of ammonium carbamoselenoates generated in situ from selenium, carbon monoxide, and secondary amines [3]. This reaction can be carried out conveniently at room temperature under atmospheric pressure of carbon monoxide. These successful results led us to examine the reaction of tellurium with carbon monoxide and amines under similar conditions, but no reaction took place and tellurium was recovered unchanged. Since this may be due to the low reactivity of tellurium, we then employed lithium amides instead of amines and found that tellurium reacts with lithium amides and carbon monoxide at low temperatures to form lithium carbamotelluroates which undergo alkylation with alkyl halides to yield Te-alkyl carbamotelluroates.A typical example is as follows. To a flamedried, 30 mL, three-necked, round bottom flask equipped with an Ar inlet, a CO inlet, and a rubber septum, 10 mL of THF and 5 mmol of piperidine were placed under Ar. The solution was cooled to -78"C, and 5.5 mmol of "BuLi (1.6 N in hexane) was injected with stirring. After 15 minutes, finely ground elemental tellurium (638 mg, 5 mmol) was added and the mixture was allowed to warm to 10°C. All of the tellurium pieces disappeared within 1 hour to give a dark violet homogeneous solution. The solution was cooled to -78°C again, purged with carbon monoxide, and stirred for 2 hours, resulting in the absorption of 129 mL (5.8 mmol) of carbon monoxide. At this stage, lithium piperidi-0 1993 VCH Publishers, Inc.

Copper(I)-Catalyzed Highly Efficient Synthesis of Benzoselenazoles and Benzotellurazoles

“…Since we already developed tellurium-assisted carbonylation and imidoylation of amines with carbon monoxide and isocyanides, respectively, starting from lithium amides, we examined the reaction using lithium amides instead of amines. Lithium piperidide, generated from piperidine and n -BuLi in the presence of HMPA at −78 °C, was allowed to react with tellurium and then isocyanide 2 and CuI (5 mol %) were added at room temperature.…”

SnCl4‐Induced Unsymmetrical Cleavage of Bis(N,N‐diethylcarbamoyltelluro)‐arylmethanes: Generation of Tellurobenzaldehydes

“…Bis( N,N ‐dimethylcarbamoyl) ditelluride ( 1 ) was at first prepared in moderate yield by treating N,N ‐dimethylformamide (DMF) with sodium and elemental tellurium under heating followed by aerobic oxidation of the reaction mixture . Preparation of bis( N,N ‐diethylcarbamoyl) ditelluride ( 2 , R 1 = C 2 H 5 ) was also carried out by treating N,N ‐diethylformamide (DEF) with lithium metal and elemental tellurium through a similar procedure as shown in Scheme .…”

“…However, only limited research works on generation, trapping, or metal complexation of telluroaldehydes B were reported due to the high instability of the target species toward air, light, and heating, as well as the lack of preparative methods of suitable and easily accessible precursors. In the course of our studies on the novel generation of higher‐row chalcogenocarbonyl compounds, we previously reported a convenient preparation of stable ditelluroacetal derivatives A through the reaction of in situ generated tellurocarbamate ions with gem‐dihaloalkanes . Actually, such ditelluroacetals A are recognized as potent precursors for telluroaldehydes B in the light of their symmetrical structures with an easily removable electron‐withdrawing carbamoyl group on each tellurium atom, and compouds A are expected to undergo SnCl 4 ‐induced unsymmetrical C–Te bond cleavage to generate telluroaldehydes B through push–pull type removal of N,N ‐diethyltellurocarbamate in an analogous manner of our previous report on the generation of selenoaldehydes from bis( N,N ‐dimethylcarbamoylseleno)methanes .…”

Multicomponent Reaction of Isocyanide, Ditelluride, and Mn(III) Carboxylate: Synthesis of N-Acyl Tellurocarbamate

“…Kambe et al found that isocyanate can react with i Bu 2 AlTeR to give tellurocarbamate after hydrolysis (Figure d) . Sonoda et al reported that lithium amides reacted with tellurium under atmospheric pressure of carbon monoxide to yield lithium carbamotelluroates which reacted with alkyl halides to give Te-alkyl tellurocarbamates (Figure e) . These methods generally require multiple steps and use of active organometallic reagents and suffer from limited scope.…”