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Enantioselective Hydrogenation of dehydro-PZQ and derivatives
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6th May 2011 @ 05:29
Experiments on the oxidation of N-benzoyl-PZQ to the enamide by molten sulfur. Repetition of Scale-up: Oxidation of N-benzoyl-PZQ by sulfur (MW59-7) to synthesize more N-benzoyl-PZQ enamide

Scheme MW59.png

See related experiments on rac-PZQ:
Sulfur melt data smogasbord
Oxidation of N-benzoyl-PZQ by sulfur (MW59-1 to MW59-6)

Hazard and Risk Assessment:
HRAF MW57.pdf

Start time: 4:20 PM 2/05/2011

A mixture of N-benzoyl-PZQ (518 mg, 1.69 mmol, M.W. 306.4 g/mol) and sulfur (108 mg, 3.38 mmol, 2 eq., M.W. 32.1 g/mol) were heated at 190°C for 2 h.
The dark brown solid was dissolved in ethyl acetate, evaporated on silica gel and purified by column chromatography (ethyl acetate: hexane, 1:1)
-TLC showed that there was still starting material left

Yield: 237 mg (780 µmol, 46%) yellow solid [M.W. 304.3 g/mol]
-> sulfur impurities

Further procedure, see: Scale-up: Oxidation of N-benzoyl-PZQ by sulfur (MW59-7)

The reaction had not gone to completion after 2 h, however an increase in reaction time / temperature would more than likely improve the yield.
Re: Repetition: Oxidation of N-benzoyl-PZQ by sulfur (MW59-8) by Matthew Todd
6th May 2011 @ 06:56
Can you expand a little on the (potential) problems of sulfur and what you did to try to remove them?