title: Harnessing the ortho-directing ability of the azetidine ring for the regioselective and exhaustive functionalization of arenes.
abstract: This work demonstrates how the directing ability of the azetidine ring could be useful for regioselective ortho-C-H functionalization of aryl compounds. Robust polar organometallic (lithiated) intermediates are involved in this synthetic strategy. The reagent n-hexyllithium emerged as a safer, yet still effective, basic reagent for the hydrogen/lithium permutation relative to the widely used reagent nBuLi. Two different reaction protocols were discovered for regioselective lithiation at the ortho positions adjacent to the azetidine ring, which served as a toolbox when other competing directing groups were installed on the aromatic ring. The coordinating ability of the azetidine nitrogen atom, as well as the involvement of dynamic phenomena related to the preferential conformations of 2-arylazetidine derivatives, were recognized to be responsible for the observed reactivity and regioselectivity. A site-selective functionalization of the aromatic ring was achieved for aryl azetidines with either coordinatively competent groups (e.g. methoxy) or inductively electron-withdrawing substituents (e.g. chlorine and fluorine). By fine-tuning the reaction conditions, regioselective introduction of several substituents on the aromatic ring could be realized. Several substitution patterns were accomplished, which included 1,2,3-trisubstitution, 1,2,3,4-tetrasubstitution, and 1,2,3,4,5-pentasubstitution, up to the exhaustive substitution of the aromatic ring.
authors.affiliation: Department of Pharmacy-Drug Sciences, University of Bari "A. Moro" Via E. Orabona 4, Bari 70125 (Italy).
authors.forename: Marina
authors.initials: M
authors.lastname: Zenzola
authors.forename: Leonardo
authors.initials: L
authors.lastname: Degennaro
authors.forename: Piera
authors.initials: P
authors.lastname: Trinchera
authors.forename: Laura
authors.initials: L
authors.lastname: Carroccia
authors.forename: Arianna
authors.initials: A
authors.lastname: Giovine
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Romanazzi
authors.forename: Piero
authors.initials: P
authors.lastname: Mastrorilli
authors.forename: Rosanna
authors.initials: R
authors.lastname: Rizzi
authors.forename: Luisa
authors.initials: L
authors.lastname: Pisano
authors.forename: Renzo
authors.initials: R
authors.lastname: Luisi
mesh_terms: D000147:Acids, Heterocyclic / Q000737:chemistry; D001384:Azetidines / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure
chemical_list: D000147:Acids, Heterocyclic; D001384:Azetidines; C082735:azetidine
keywords: azetidines; dynamic reactivity; heterocycles; lithiation; regioselectivity