1‐Phosphabicyclo[3.2.1]octane

1‐Phosphabicyclo3.2.1]octanes 1‐Phosphabicyclo3.2.1]octane has been obtained by free‐radical cyclization of (2‐vinyl‐4‐pentenyl)‐phosphane in the presence of AIBN. Another approach to 1‐phosphabicyclo3.2.1]octanes involves free‐radical cyclization of 2‐methyl‐4‐(2‐propenyl)‐phospholane synthesized by the reaction of 2‐(2‐propenyl)‐4‐pentenyl]‐phosphane with KPH₂/18]crown‐6 in THF. The bicyclic phosphanes are characterized by reactions with CS₂, selenium, sulfur, NO, CH₃I, and HSO₃F, respectively, structural and analytical data as well as ¹H, ¹³C, ³¹P, ⁷⁷Se NMR spectral measurements. The steric crowding of the phosphanes as complex ligands has been estimated from ³¹P–¹H coupling constants according to the Tolman model. The configuration of the methyl substituents as well as the conformation of the six‐membered ring were determined by NMR parameters (coupling constants, noe's) and proved by X‐ray crystal structure analysis.