TfOH mediated intermolecular electrocyclization for the synthesis of pyrazolines and its application in alkaloid synthesis

Abstract

A metal free and green synthetic methodology employing aldehydes, phenylhydrazine and styrene mediated by TfOH has been developed to access 1,3,5-trisubstituted pyrazolines. The synthetic application of the methodology is demonstrated in the synthesis of a pyrazoline alkaloid.

Diffusion mixing with a volatile tertiary amine as a very efficient technique for 1,3-dipolar cycloaddition reactions proceeding via dehydrohalogenation of stable precursors of reactive dipoles

“…S4 and S5); in the cases of pyrazolines 8d and e, their NMR spectra coincided with those described in the literature. 32,39 In the case of volatile olefins 2 and 3, both diffusion of triethylamine into the reaction mixture and reverse diffusion of norbornene 2 or norbornadiene 3 into the external aminecontaining vial occurred during the reaction. However, when a 3-fold excess of alkenes was used, the resulting dipoles had the possibility to completely react with the olefin in the inner vessel, and the target heterocycles 9 and 10 were obtained in good yields (Scheme 3).…”

“…S4 and S5); in the cases of pyrazolines 8d and e , their NMR spectra coincided with those described in the literature. 32,39…”

1,3,5‐Triphenylpyrazoline‐Based Organocatalysis: Synthesis of Aryl‐Heteroaryl Compounds and Exploiting By‐Product from the Reaction for Alkyne‐Carbonyl Metathesis (ACM) Reaction in One Pot

“…For better understanding of the catalytic activity of pyrazoline molecule, various substituted pyrazoline molecules have been synthesized (Scheme ) . The absence of hydroxyl group in catalyst 2 , lowered the yield to 60% (entry 7, Table ), proving the role of OH in stabilization of radical cation ( 1 a ) by intramolecular hydrogen bonding.…”

Deep Eutectic Solvent Mediated Alkyne‐Carbonyl Metathesis (ACM) Reaction for the Synthesis of 2H‐Chromene Derivatives

“…Besides, trace amount of product observed at little higher temperature in ChCl:Urea (entry 2), other DES such as ChCl:Gylcerol, ChCl:ethylene glycol were failed to produce the chromene product (entry 3 & 4). Next, we prepared acidic DES ChCl: p TSA and performed the reaction. As expected, complete conversion was observed through TLC technique over the period of 8 h at 45–50 °C.…”