A chiral phase-transfer catalyst was used to add hydroxylamine to the enone then dehydrate to produce the optically active 4H-isoxazole with 85.2% ee. The chiral PTC was anthracenylmethyl quininium chloride. Since there are several reaction steps after this intermediate, enantiomer purification was achieved in a later step.
In many chiral PTC-base reactions, the hydroxyl of the quininium salt can be deprotonated by the base and the alkoxide of the quininium salt serves as the base that actually deprotonates the substrate. In this case, it is likely that the cesium hydroxide deprotonates the hydroxylamine and the only role of the chiral PTC is to bring the aminoalkoxide in contact with the enone.
If you need expert help choosing phase-transfer catalysis conditions to achieve low-cost high-performance green chemistry for PTC-base applications, now contact Marc Halpern of PTC Organics to inquire about collaboration.
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!).
