Phosphonium- and Benzotriazolyloxy-Mediated Bond-Forming Reactions and Their Synthetic Applications

Phosphonium and benzotriazolyloxy (and related) intermediatesare easily prepared by the reactions of cyclic amides and ureaswith (1 H-benzotriazol-1-yloxy)triaminophosphonium hexafluorophosphaterelated reagents. The former intermediates could also be made availableusing analogous phosphonium reagents prepared in situ or from commercialsources. These intermediates efficiently lead to carbon-nitrogen,carbon-oxygen, carbon-sulfur, and carbon-carbonbond formations through nucleophilic aromatic substitution reactionswith various nucleophiles. A new -reaction involving thegeneration of phenols in situ from arylboronic acids and oxygenunder palladium(0) catalysis or with boronic acids and hydrogenperoxide is reviewed. 1 Introduction 2 Phosphonium-Mediated Nucleophilic Aromatic Substitution Reactionsof Heterocyclic Systems 2.1 Phosphonium-Mediated Carbon-Nitrogen Bond Forming Reactionsvia Modified Appel Conditions 2.2 Phosphonium-Mediated Carbon-Nitrogen Bond Forming Reactionsvia Commercially Available Phosphonium Reagents 2.2.1(1 H-Benzotriazol-1-yloxy)tris(dimethylamino)phosphoniumHexafluorophosphate as an Activating Agent 2.2.2(1 H-Benzotriazol-1-yloxy)tripyrrolidinylphosphonium Hexafluorophosphateand Bromotripyrrolidinylphosphonium Hexafluorophosphate as ActivatingAgents 2.2.3 Solvent and Base Effects 2.3 Reactivity of Various Phosphonium Reagents 2.4 Phosphonium-Mediated Carbon-Oxygen, Carbon-Sulfur, andCarbon-Carbon Bond Forming Reactions 3 Benzotriazolyloxy-Mediated and Related Bond-Forming Reactionsof Heterocyclic Systems 4 Phosphonium-Mediated Reaction Mechanisms 4.1 Stepwise Pathways via Phosphonium and 1 H-Benzotriazol-1-ol(or Pyridotriazol-1-ol) Adducts 4.2 1 H-Benzotriazol-1-ol (or Pyridotriazol-1-ol)Adduct Independent Pathway 5 Palladium-Catalyzed Heteroaryl Ether Formation from Benzotriazolyloxy-or Pyridotriazolyloxy-Substituted Heterocycles with ArylboronicAcids 6 Unusual 1 H-Benzotriazol-1-ol AdductRearrangement 7 A Tentative Protection and Amination Strategy Involving a 1 H-Benzotriazol-1-ol Adduct 8 Conclusion and Outlook