Pyrroles catalytic dehydrogenation

Experiments on the synthesis of 4,5,6,7-tetrahydroindole and 1 -vinyl-4, 5,6,7-tetrahydroindole from cyclohexanone oxime and acetylene on bench reactors of 5 and 25 L performed under a 1.5 atm pressure give positive answers to these questions. Thus, at 100°C and KOH concentration of 0.4 mol/L, the output of 1 L of catalyst solution can amount to 50-100 g of pyrroles per hour. This means that in a small 1 m3 reactor, it is possible to produce up to 400 tons of 4,5,6,7-tetrahydroindoles (1 and/or 2) per year, which is quite acceptable to meet an initial demand for these products. It can initiate, for instance, a cheap indole manufacture by catalytic dehydrogenation of tetrahydroindoles 1 and 2. 

Pyrrole synthesis via catalytic dehydrogenation has also received considerable attention. Traditional approaches, such as the Hantzsch and Paal-Knorr pyrrole syntheses, rely on the use of pre-functionalised substrates (Scheme 12.36). In addition, the Hantzsch pyrrole synthesis generates halide waste. 

Secondaiy alcohols have been shown to be competent reaction partners for the preparation of tertiaiy amines, but typically require higher temperatures. Beller and co-workers reported a method for the synthesis of cx-branched tertiary amines via N-all lation of secondary amines with secondaiy alcohols using catalytic Ru3(CO)i2 with JV-phenyl-2-(dicyclo-he)ylphosphanyl)pyrrole ligand (Scheme 12.6). The scope is limited to the adulation of cyclic amines as acyclic amines undergo trans-alkylation, likely due to competitive amine dehydrogenation. 

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