Synthesis of hexa(methyl/phenyl) substituted pyrazolines and thermolysis to hexasubstituted cyclopropanes

✍ Scribed by Alfons L. Baumstark; G. Davon Kennedy; P. C. Vasquez; N. Desalegn; Phong Truong

• Book ID: 102342094
• Publisher: Journal of Heterocyclic Chemistry
• Year: 2010
• Tongue: English
• Weight: 112 KB
• Volume: 47
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.266

✦ Synopsis

Abstract

magnified image Addition of methyllithium to the 3‐position of 4,5‐dihydro‐3,4,4,5,5‐pentasubstituted‐N‐tosyl‐1H‐pyrazoles [1a 4,4,5,5‐tetramethyl‐3‐phenyl; 1b 4,4,5‐trimethyl‐3,5‐diphenyl; 1c 4,4‐dimethyl‐3,5,5‐triphenyl] produced the corresponding hexasubstituted pyrazolines, 2a, 2b, 2c, as the only isolable products. For 2b, the 3,5‐phenyl groups were found to be exclusively cis, indicative of facial specificity for the addition reaction. The reaction of phenyllithium with 1b yielded 2c as the minor product. For phenyllithium addition, direct attack on sulfur of the tosyl group with subsequent loss of phenyl p‐tolylsulfone was the major pathway vs. the S~N~2i attack at carbon‐3. Thermolysis of pyrazolines 2a, 2b, 2c, at 200°C, smoothly produced the hexasubstituted cyclopropanes [3a 1,1,2,2,3‐pentamethyl‐3‐phenylcyclopropane; 3b cis‐1,1,2,3‐tetramethyl‐2,3‐diphenylcyclopropane; 3c 1,1,2‐trimethyl‐2,3,3‐triphenylcyclopropane] in excellent yield. J. Heterocyclic Chem., (2010).