Nucleophilic Reactivities and Lewis Basicities of 2‐Imidazolines and Related N‐Heterocyclic Compounds. Issue 16 (9th April 2013)

• Record Type: Journal Article
• Authors: Maji, Biplab; Baidya, Mahiuddin; Ammer, Johannes; Kobayashi, Shinjiro; Mayer, Peter; Ofial, Armin R.; Mayr, Herbert
• Is Part Of: European journal of organic chemistry. Issue 16(2013)
• Page Start: 3369
• Page End: 3377
• Publication Date: 2013-04-09
• Subjects: Kinetics -- Structure–reactivity relationships -- Lewis basicities -- Thermodynamics -- Nucleophilic addition -- ­Organocatalysis; Chemistry, Organic -- Periodicals; Organic compounds -- Synthesis -- Periodicals; Bioorganic chemistry -- Periodicals; Chemistry, Physical organic -- Periodicals; 547
• DOI: 10.1002/ejoc.201300213
• Languages: English
• ISSNs: 1434-193X

Abstract

Abstract: The nucleophilicity parameters N and s N, as defined by the linear free‐energy equation log k (20 °C) = s N ( N + E ), of the 2‐imidazolines1a –d and the related N‐heterocyclic compounds2 –5 have been determined by studying the rates of their reactions with differently substituted benzhydrylium ions in dichloromethane at 20 °C by stopped‐flow or laser flash photolysis techniques. It is demonstrated that the N and s N parameters thus obtained can be used to reliably predict the rate constants for their reactions with Michael acceptors of known electrophilicity E . A comparison of the nucleophilicity parameters of the imidazoline derivatives1 with other commonly used nucleophilic organocatalysts shows that they are 10 to 10 3 times less nucleophilic than PPh3, 1, 8‐diazabicyclo[5.4.0]undec‐7‐ene, or 4‐(dimethylamino)pyridine. The structure–reactivity relationships of these heterocycles are discussed. Abstract : Rate and equilibrium constants for the reactions of 2‐imidazolines and related N‐heterocyclic compounds with diarylcarbenium ions have been measured in CH2 Cl2 at 20 °C. These data were employed to determine their nucleophilicities and Lewis basicities, which were compared with other nucleophilic organocatalysts.