This chapter covers recent developments in the title area published during 2020. The past year has seen an increase in the number of papers including the synthesis, properties, and reactivity of novel five-coordinated compounds. In this respect, there have been two papers highlighting methods for the synthesis and properties of azaphosphatranes.^1,2  Well-known topics including the synthesis and reactivity of cage-phosphoranes,³  spirophosphoranes derived from α-amino acids⁵  as well as other spirophosphoranes^4,6,8–10  and fluorophosphoranes⁷  have also appeared recently. Moreover, the reactivity of pentacoordinate phosphoranes toward selected metal halides has also been discussed.¹¹ 

Furthermore, experimental and theoretical insights into reaction mechanisms in which five-coordinated species are involved have been presented. Among them, the most significant examples include synthetic routes to dibenzophospholes,¹²  carbofluorination of alkynes,¹³  hydrolysis of phosphonium bromides,¹⁴  Wittig-type syntheses of 2-phenylbenzofurans¹⁵  and pyrazolodienoates,¹⁶  as well as O-phosphination reactions of aldehydes and ketones¹⁷  and in catalytic Mitsunobu reactions.¹⁸