An Efficient One Pot Synthesis of New Indanopyrazoline and Indanopyrazole Derivatives

Abstract

Synthesis of a series of novel fused pyrazolines and pyrazoles has been accomplished in good yields by regioand diastereoselective 1,3-dipolar cycloaddition of enamines of indan-1-one 1a-c towards C-aryl-N-phenylnitrilimines 2d-f. The structure of the cycloadducts was elucidated by 1D and 2D NMR studies.

Regioselective Synthesis of Mono‐ and Dispiropyrazoline Derivatives via 1,3‐dipolar Cycloaddition with Nitrilimines

“…Thus, the signal for C 4 appears at δ 65.7 ppm and δ 63.1 ppm, respectively; the quaternary spirocarbons C 3ʹ/5ʹ resonate at δ 82.8 ppm and δ 80.0 ppm. These chemical shifts are in agreement with our earlier studies and the literature data .…”

1,3‐Dipolar Cycloaddition Reactions of Indan‐1‐one Enamines across Arylnitrile Oxides Leading to Novel Cyclic Isoxazoline Derivatives

“…The observed regiochemistry was also confirmed by the 13 C NMR chemical shifts of the carbon atoms (C‐3a), which resonate around δ = 43–47 ppm. This range is in agreement with the remoteness from the isoxazolinic oxygen atom . In the case of the hypothetical isomeric structures 4'ad , 4'ae , 4'af , 4'ag , 4'ah , 4'bd , 4'be , 4'bf , 4'bg , 4'bh , 4'cd , 4'ce , 4'cf , 4'cg , 4'ch , the chemical shift values of the doublet assigned to the carbon atoms (C‐8a) attached to oxygen atom should be inferior to 76.7 ppm .…”

“…This excludes the presence of the inverse regioisomers 4'ad , 4'ae , 4'af , 4'ag , 4'ah , 4'bd , 4'be , 4'bf , 4'bg , 4'bh , 4'cd , 4'ce , 4'cf , 4'cg , 4'ch . In this case, one should expect a chemical shift value higher than 5 ppm because of the proximity of the isoxazolinic oxygen atom . The observed regiochemistry was also confirmed by the 13 C NMR chemical shifts of the carbon atoms (C‐3a), which resonate around δ = 43–47 ppm.…”

“…The reaction leads to a stable zwitterionic nitrilimine‐enamine cycloadduct . In a previous paper, we have also shown that the cycloaddition of arylnitrile oxides across unsubstituted indan‐1‐one enamines proceeds with complete regioselectivity, without loss of the amino group as it was observed in the case of 1‐tetralone and 2‐tetralone enamines .…”

“…Very recently, we reported the high‐yield synthesis of a series of novel fused pyrrazolines and pyrazoles by regioselective 1,3‐dipolar cycloaddition of these dipolarophiles toward C ‐aryl‐ N ‐phenylnitrilimines . The two dipolarophilic faces of the unsubstituted indan‐1‐one enamines used in our previous study are not diastereotopic.…”