Trimethylsily lacetylene

Abstract The coupling of 2-azabicyclo[2.2.1]hept-5-en-3-one and trimethylsily-lacetylene or phei rlacetylene under Domino Heck conditions gives compounds 2a-c and 4a-c in moderate yields and cyclopentene derivatives, 3a-c in low yields. The procedure can be of use for the synthesis of alkynyl bicyclic lactams. 

We continued our work with the reductive Heck and Domino-Heck reactions [1, 7J of new bicyclic compound (3) by treating it with different aryl- and hetaryl-iodides, as a result a series of new epibatidine analogues were synthesized, continuously separated and purificated by column chromatography on silica gel. Treatment of 3 with iodobenzene, 2-iodothiophene, 1-iodonapthalene and 2-chloro-5-iodopy-ridine under reductive Heck conditions gave new compounds 4a-d and 5b, 5d as exo-regioisomers after chromatographic separations. The reactions with iodobenzene and 1-iodonapthalene gave only 5-exo- products. The use of trimethylsily-lacetylene under Domino-Heck conditions provided alkynic bicyclic systems 6e andf. 

As expected, hydrogen phosphinate, which is a hybrid structure of hydrogen phosphonate and secondary phosphine oxide, adds to alkynes in the presence of the Pd-diphenylphosphinic acid catalyst system (Scheme 44) [36]. Normally, branched isomers are the major products, while trimethylsily-lacetylene exceptionally affords the corresponding terminally phosphinylat-ed product. Diphenylacetylene also reacts to afford the corresponding adduct in 99% yield. 

H-l,3-ditellurole. Under an atmosphere of argon, 0.23 g (2.4 mmol) of trimethylsily-lacetylene are dissolved in 5 mL dry tetrahydrofuran. The solution is cooled to -70°C. n-Butyl lithium (1.0 mL, 2.4 M, 24 mmol) is dropped into the stirred solution. Then 0.20 g (2.0 mmol) of tellurium powder is added. The mixture is warmed to 20°C and kept at this temperature for 2 h. To this mixture, cooled again to -70°C, is added a solution of 0.35 g (2.0 mmol) of chloroiodomethane in 1 mL of tetrahydrofuran. The mixture is stirred for 15 min and then quenched with 50 mL water. The product is extracted with three 15 mL portions of dichloromethane. The combined extracts are washed with brine, dried with anhydrous sodium sulphate and filtered. The filtrate is concentrated to give trimethylsilylethynyl chloromethyl tellurium as a pale-yellow oil. Tellurium powder (0.125 g, 1.0 mmol) is added to 2 mL of a 1 M solution (2.0 mmol) of lithium triethylborohydride in ethanol. The mixture is stirred at 20°C for 2 h under an atmosphere of argon. Then 2 mL of 1 M sodinm ethoxide in ethanol are added followed by 0.27 g (1.0 mmol) of trimethylsilylethynyl chloromethyl tellurium dissolved in 2 mL dimethylformamide. The mixture is stirred for 15 h at 20°C, then diluted with 25 mL water and extracted with three 15 mL portions of dichloromethane. The combined extracts are dried with anhydrons sodinm snlphate, fdtered and the filtrate concentrated. The residue is chromatographed on silica gel with hexane/dichloromethane (1 1) as mobile phase. The fractions containing the prodnct are concentrated and recrystallized from methanol 65% yield, m.p. 85°C. 

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