517 Heteroatom Chemistry Volume 9, Number 5, 1998 Synthesis of Spiropyrazolines Muthian Shanmugasundaram, 1 Raghavachary Raghunathan, 1 and Ezekiel J. Padma Malar 2 1 Department of Organic Chemistry, University of Madras, A.C. College Campus, Chennai 600 025, Tamil Nadu, India 2 Department of Physical Chemistry, University of Madras, A.C. College Campus, Chennai 600 025, Tamil Nadu, India Received 9 December 1997 ABSTRACT: Synthesis of a series of novel 1,3,2'-tri- phenyl-4-aryl spiropyrazolines [5.4']-2'-butenolides has been accomplished in good yield by regioselective 1,3-dipolar cycloaddition of diphenylnitrilimine with (E)-3-arylidenebutenolides. X-ray crystal structure analysis of one of the products 4a confirms the struc- ture of the product and the regiochemistry of cycload- dition.  1998 John Wiley & Sons, Inc. Heteroatom Chem 9:517–522, 1998 INTRODUCTION In recent years, we have witnessed a significant in- crease in the utilization of 1,3-dipolar cycloaddition reaction as a useful methodology for the synthesis of novel heterocycles [1]. The regio- and stereoselection in these types of reactions have resulted in an elegant application in the synthesis of natural products [2]. Many pyrazoline derivatives have an important bio- logical activity (e.g., as anti-inflammatory, analget- ics, and herbicides), and their synthesis has attracted much attention [3]. Butenolide heterocycles have drawn much attention owing to their important pharmacological properties [4]. As part of our en- deavor to explore the synthetic potentiality in the construction of novel pyrazoline derivatives [5,6] and also to study their biological applications, we have undertaken a systematic study of the reactions Correspondence to: Raghavachary Raghunathan.  1998 John Wiley & Sons, Inc. CCC 1042-7163/98/050517-06 of the versatile 1,3-dipole diphenylnitrilimine (DPNI) with various 3-arylidenebutenolides. In the present study, we discuss 1,3-dipolar cy- cloaddition reactions of DPNI with 3-arylidenebu- tenolides. The Frontier Molecular Orbital method has been used to study the regiochemistry of cycloaddition. RESULTS AND DISCUSSION In an attempt to evaluate the effect of the presence of electron-donating and electron-withdrawing groups in direct conjugation with the double bond of the dipolarophile on the regioselectivity in the cy- cloaddition reactions, we have studied the reactions of DPNI with -arylidene-c-phenyl-D bc butenolides, resulting in the formation of novel spiropyrazolines in good yields (Scheme 1). The addition is highly re- gioselective to give a single product exclusively in each of the cases that we have studied. The 3-arylidenebutenolides were prepared by the condensation of b-benzoylpropionic acid with ar- omatic aldehydes in the presence of acetic anhydride and sodium acetate by the Perkin Erlenmeyer reac- tion [7], and the products were assigned the E con- figuration on the basis of their NMR spectra, in ac- cordance with a literature report [8,9]. Reactions of 3-arylidenebutenolides with DPNI (generated in situ from N-phenylbenzhydrazidoyl chloride in chloro- form solution in the presence of triethylamine at room temperature) led to the formation of 1:1 ad- ducts as a single product in each case, as evidenced