Pictet-Spengler route to Praziquantel

 

Mnr: 1-10



Hazard and Risk Assessment:


A solution of 3,4-dimethoxyphenethylamine (24.0 mL, 132 mmol) in ethyl formate (130 mL, 1590 mmol) was heated to reflux for 13 h. The remaining ethyl formate and the by-product ethanol were removed under reduced pressure to give yellow liquid.

The crude 2-(3,4-Dimethoxyphenyl)ethylformamide and triethylamine (55.4 mL, 397 mmol) were dissoved in dry DCM (240 mL) and phosphoryl chloride (12.3 mL, 132 mmol) was added dropwise added at 0°C. The mixture was then stirred for 1 h at 0°C and a further 4 h at room temperature.
The mixture was quenched with water and neutralized with NaHCO3 solution. The organic layer was separated and the aqueous solution was extracted DCM (250 mL x4). The organic layers were combined, dried over magnesium sulphate, filtered and evaporated afforded a dark brown oil.

Crude:- 30.519 g

Column:- 25-33% EtOAc/Hex

Frac 3-5 :- 21.751 g as a pale yellow oil (86 %)

Characterisation



1H NMR (500 MHz, CDCl3): d = 6.84 (d, J = 8.7 Hz, 1H), 6.81-6.76 (m, 2H), 3.88 (s, 3H), 3.86 (s, 3H), 3.59 (t, J = 6.9 Hz, 2H), 2.91 (t, J = 6.9 Hz, 2H).




13C NMR (75 MHz, CDCl3): d= 156.4 (t, J = 5.2 Hz), 149.4, 148.3, 129.4, 120.9, 112.0, 111.4, 56.0, 43.4 (t, J = 6.3 Hz), 35.4.

HRMS (ESI (+)) Calcd. for [C33H40N3O6]+ (for [3M+H]+): 574.2912, found: 574.2914.



Vmax/cm-1 2939, 2147, 1515.

Preparation of 2-(3,4-Dimethoxyphenyl)ethyl isocyanide (MW37)



Lab book page complete, MNR