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17th February 2011 @ 08:19
Attempts to the acid-mediated cyclization of the N-benzoyl-protected Ugi intermediate MW51-1 with methanesulfonic acid

See also:
Attempts to the Bronstedt-acid catalysed Pictet-Spengler cyclization using BINOL-N-triflyl phosphoramide (MW41)
Cleavage of the dimethoxy acetal of 2-((2,2-dimethoxyethyl)amino)-N-phenethylacetamide hydrochloride MW7(MW42)

Reaction Scheme


Hazard and Risk Assessment:
HRAF MW53.pdf


MW53-1:
Start time: 7:30 PM 17/02/2011
End time: 10:10 PM 21/02/2011
MW51-1 (31 mg, 83.8 µmol, M.W. 370.4 g/mol) was stirred with methanesulfonic acid (0.5 mL) for 15 h at room temperature.
- work-up: neutralized with Na2CO3, extracted with DCM, dried with Na2SO4, evaporated
Data: 1H NMR MW53-1.pdf

MW53-2:
Start time: 7:30 PM 17/02/2011
End time: 9:30 PM 21/02/2011
MW51-1 (29 mg, 78.4 µmol, M.W. 370.4 g/mol) was stirred with formic acid (0.5 mL) for 4 days at room temperature.
- work-up: neutralized with Na2CO3, extracted with DCM, dried with Na2SO4, evaporated
Data: 1H NMR MW53-2.pdf

MW53-3:
Start time: 7:15 PM 21/02/2011
End time: 9:30 PM 22/02/2011
MW51-1 (31 mg, 83.8 µmol, M.W. 370.4 g/mol) was stirred with methanesulfonic acid (0.5 mL) for 14 h at 60°C.
- work-up: neutralized with Na2CO3, extracted with DCM, dried with Na2SO4, evaporated
TLC: Rf=0.43 (ethyl acetate, 100%, stain ceric ammonium molybdate)- no starting material
Data: 1H NMR MW53-3.pdf: no specific signals because of rotamers

TLC: (Rf=0.43; ethyl acetate, 100%, stain: potassium permanganate), same Rf for starting material and product, product stains without heating.
- Stain: ceric ammonium molybdate: product doesn't stain.
TLC MW53.JPG


Results:
MW53-1: still starting material, + side products. (after 12 h - no product visible)
MW53-2: colourful reaction, no visible starting material, lots of side product (after 2 d - product and a lot of side product)
MW53-3: look like a clean reaction (product - almost clean reaction)


References:
[1] Polycyclic Compounds by Ugi−Pictet−Spengler Sequence, W. Wang†, S. Ollio†, E. Herdtweck and A. Doemling, J. Org. Chem. 2011, 76 (2), pp 637–644. (DOI: 10.1021/jo102058s)
Linked Posts
Attached Files
Reaction Scheme
HRAF MW53.pdf
1H NMR MW53-1.pdf
1H NMR MW53-2.pdf
1H NMR MW53-3.pdf
TLC MW53.JPG