Abstract
TfOH mediated easy access to interesting pyrazolines starting from an aldehyde, phenylhydrazine and styrene has been developed. The scope of this synthetic methodology has been explored by synthesizing various 1,3,5-trisubstituted pyrazolines in very good yields with very high regioselectivity. The origin of regioselectivity has been explained by comparing the stability of possible intermediate carbocations. The synthetic utility of a green solvent has been explored by synthesizing some of pyrazolines in a DES medium. The synthetic application of the present methodology is employed in the synthesis of a pyrazoline alkaloid.
Highlights
TfOH mediated easy access to interesting pyrazolines starting from an aldehyde, phenylhydrazine and styrene has been developed
A few representative examples of biologically and medicinally important pyrazoles and pyrazolines are given in Fig. 1.5–7 In particular, considerable interest has been focused on 1,3,5-trisubstituted pyrazoline derivatives due their potential pharmacological activities including (i) antitubercular activity against the H37Rv strain of Mycobacterium,[9] (ii) antiproliferative activity,[8,10] (iii) antibacterial activity,[11,12,13] (iv) antiobesity effect in an animal model of the potent cannabinoid CB1 receptor antagonist,[14] (v) pre-emergent herbicide activity against various kinds of weeds,[15] and (vi) ACE-inhibitory activity with 0.123 mM IC504.16 Pyrazoline derivatives show enhanced biological activity compared with their corresponding pyrazoles.[17]
A regioselective tandem one-pot intermolecular electrocyclization reaction under metal free condition to access 1,3,5-trisubstituted pyrazolines would be of great importance
Summary
TfOH mediated easy access to interesting pyrazolines starting from an aldehyde, phenylhydrazine and styrene has been developed. We are disclosing a general, metal free and green synthetic methodology to access diverse pyrazoline derivatives with various functionalities including –NO2, –OH and aliphatic groups using arylhydrazines, aldehydes and styrenes. We have obtained the corresponding pyrazoline products in very good yields with enhanced regioselectivity.
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