Intramolecular Nucleophilic Vinylic Substitution (S_NV) by Carbon Nucleophiles: Conformationally Directed Formation of Dienes from N,N’-Diallyl Ureas

Nucleophilic vinylic substitution (S_NV) by carbon nucleophiles allows the formation of vinylic C−C bonds without transition metal catalysts. In this paper, we show that tethering two alkenes together through a urea linkage can lead to the formation of a diene by an intramolecular S_NV reaction. The starting materials are fully substituted N,N’-diallyl ureas; the reaction proceeds in the presence of base, and entails a cascade of deprotonations, reprotonations, and an S_NV reaction of an allylic carbanion on a rare electrophile: a vinylic urea. As a result, two allylic substituents couple to form a diene, despite the fact that neither is activated towards electrophilic attack. The reaction is tolerant of significant steric bulk, and exhibits regioselectivity with unsymmetrical diallyl ureas: β-substituted allyl groups invariably behave as nucleophiles, while electrophilic behavior may be enforced by the use of an E-vinylic urea substituent that cannot be deprotonated under the reaction conditions.