In the reaction shown in the diagram, tetrabutylammonium iodide was used as a reagent, not as a phase-transfer catalyst to form N-iodopiperdine from N-chloropiperidine. Iodopiperdine added across the terminal double bond of the allene. The second step was an N-alkylation with 1-phenylpiperazine reacting with the iodomethyl group.
The two reactions were performed in one pot without any workup (no isolation of intermediate), so the tetrabutylammonium cation was still present during the second step. It is possibly that the quat assisted the N-alkylation, though the activity of cesium carbonate in acetonitrile may have been sufficient without assistance of the quat.
Notably, without TBAI, the yield was lower than 5%. When amount of TBAI was reduced from 1.5 equiv. to 0.5 equiv., the yield dropped to 41%. This likely suggests that the iodide was crucial and not the tetrabutylammonium.
Cesium carbonate was superior to other bases including potassium carbonate. THF was less effective than acetonitrile as solvent.
About Marc Halpern
Dr. Halpern is founder and president of PTC Organics, Inc., the only company dedicated exclusively to developing low-cost high-performance green chemistry processes for the manufacture of organic chemicals using Phase Transfer Catalysis. Dr. Halpern has innovated PTC breakthroughs for pharmaceuticals, agrochemicals, petrochemicals, monomers, polymers, flavors & fragrances, dyes & pigments and solvents. Dr. Halpern has provided PTC services on-site at more than 260 industrial process R&D departments in 37 countries and has helped chemical companies save > $200 million. Dr. Halpern co-authored five books including the best-selling “Phase-Transfer Catalysis: Fundamentals, Applications and Industrial Perspectives” and has presented the 2-day course “Practical Phase-Transfer Catalysis” at 50 locations in the US, Europe and Asia.
Dr. Halpern founded the journal “Industrial Phase-Transfer Catalysis” and “The PTC Tip of the Month” enjoyed by 2,100 qualified subscribers, now beyond 130 issues. In 2014, Dr. Halpern is celebrating his 30th year in the chemical industry, including serving as a process chemist at Dow Chemical, a supervisor of process chemistry at ICI, Director of R&D at Sybron Chemicals and founder and president of PTC Organics Inc. (15 years) and PTC Communications Inc. (20 years). Dr. Halpern also co-founded PTC Interface Inc. in 1989 and PTC Value Recovery Inc. in 1999. His academic breakthroughs include the PTC pKa Guidelines, the q-value for quat accessibility and he has achieved industrial PTC breakthroughs for a dozen strong base reactions as well as esterifications, transesterifications, epoxidations and chloromethylations plus contributed to more than 100 other industrial PTC process development projects.
Dr. Halpern has dedicated his adult life to his family and to phase-transfer catalysis (in that order!).
