Synthesis of 6- and 7-Membered P-Heterocycles by Ring Enlargement

This review summarizes synthetic methods affording di- and tetrahydrophosphinine oxides from phosphole derivatives and those resulting in phosphepine derivatives from 5- and 6-membered ring starting materials. The utilization of dihydrophosphinine oxides in the preparation of other phosphinine derivatives is also shown. 1. Introduction 2. Synthesis of Phosphinine Derivatives 2.1. From Phospholes Through Phospholium Salts 2.1.1. Through Halomethyl- or Alkenylphospholium Salts 2.1.2. Through Acylphospholium Salts 2.2. By the Reaction of Phospholes with Dimethyl Acetylenedicarboxylate 2.3. From a Fulvalene Ylide by Rearrangement 2.4. From 3-Methyl-2,5-dihydro-1H-phosphole 1-Oxides by Ozonolysis Followed by Aldol Condensation 2.5. From Phosphole and 2,5-Dihydro-1H-phosphole Derivatives by Incorporating a Carbene Unit 2.5.1. From Phosphole Derivatives by Reaction with Diazo Compounds 2.5.2. From 2,5-Dihydro-1H-phosphole 1-oxides by the Dichlorocarbene Approach 3. Synthesis of Phosphepine Derivatives 3.1. From Phosphole and Diyhdrophosphole Derivatives by the Introduction of a Two-Carbon Unit 3.2. From Phosphinine Derivatives