STARK ENTERPRISES

Discuss key differences between the NMR spectral data of 5 and that of the authentic natural product pipercyclobutanamide A.

Synthetic Pipercyclobutanamide A (CDCl₃, 400MHz)	Natural Pipercyclobutanamide A (CDCl₃, 400MHz)

6.89 (d, J = 1.6 Hz, 1H)	6.83 (d, J = 1.5 Hz)
6.84 (d, J = 1.7 Hz, 1H)	6.81 (s)
6.78 (dd, J = 8.0, 2.1 Hz, 1H)	6.81 (d, J = 1.5 Hz)
6.77 (dd, J = 8.0, 2.0 Hz, 1H)	6.69 (d, J = 7.9 Hz)
6.72 (d, J = 8.0 Hz, 1H)	6.65 (d, J = 2.0 Hz)
6.71 (d, J = 8.0 Hz, 1H)	6.64 (dd, J = 7.9, 2.0 Hz)
6.45 (d, J = 15.7 Hz, 1H)	6.32 (dd, J = 15.6 Hz)
6.12 (ddd, J = 15.8, 5.5, 1.8 Hz, 1H)	5.99 (d, J = 1.4 Hz)
5.99 (d, J = 11.5 Hz, 1H)	5.96 (d, J = 1.4 Hz)
5.92 (s, 2H)	5.92 (s)
5.92-5.85 (m, 3H)	5.86 (ddd, J = 10.0, 4.9, 2.7 Hz)
	5.75 (dt, J = 10.0, 1.7 Hz)
	5.21 (dd, J = 15.6, 10.2 Hz)
	4.14 (dddf, J = 9.6, 2.7, 2.7, 1.7 Hz)
3.74 (dd, J = 10.8, 8.0 Hz, 1H)	3.66 (dd, J = 11.7, 9.6 Hz)
3.66-3.57 (m, 1H)	3.56 (m)
3.52-3.38 (m, 4H)	3.48 (dddd, J = 5.6, 4.9, 2.7, 1.7 Hz)
3.27-3.06 (m, 4H)	3.31 (m)
3.05-2.93 (m, 2H)	2.93 (ddd, J = 11.7, 10.2, 5.6 Hz)
1.57-1.37 (m, 8H)	1.62 (m)
1.34-1.19 (m, 4H)	1.3-1.6 (m)

The main differences in the spectra for the synthetic and natural compounds are in the presence of a singlet at 6.81 ppm in the natural product, which does not match well to any peaks in the synthetic spectrum (although it is assumed to be one of the aromatic hydrogens).

All shifts tend to match up well, as do coupling constants in most cases. The spectrum for the pure product seems to be much more well-defined, especially in the area of the multiplet between 5 and 6 ppm (absorbing as much more complex coupling patterns). Finally, there is a peak at 4.14 in the spectrum of the pure product that is nowhere in the spectrum of the synthetic product.