Pd(0)-Catalyzed Intramolecular “Ylide-Ullmann-Type” Cyclization of Carbonyl-Stabilized Phosphonium Ylides and Access to Phosphachromones by Exocyclic P–C Cleavage

Abstract

An unprecedented palladium-catalyzed intramolecular Ullmann-type cyclization of carbonyl-stabilized phosphonium ylides with aryl bromides was successfully developed. Furthermore, a base-promoted chemoselective hydrolysis of exocyclic P–C bond of the corresponding phosphonium salts delivered various phosphachromones. Excellent selectivity and high efficiency and good functional group tolerance were observed.

Aryne-Induced SNAr/Dearylation Strategy for the Synthesis of Fluorinated Dibenzophospholes from Triarylphosphines via a P(V) Intermediate

“…The treatment of 3 with BF 3 ·OEt 2 (1 equiv) afforded the phosphonium salt 7 in quantitative yield, the structure of which was determined to be tetrahedral by X-ray crystallographic analysis (see the Supporting Information). When the fluorophosphorane 3 was treated with a few drops of H 2 O, the dibenzophosphole oxide 8aa was formed quantitatively via the loss of pentafluorobenzene 9 . In contrast, the fluorophosphorane 5 afforded the biphenylphosphosphine oxide 10 (54%) upon treatment with H 2 O, with an endocyclic C­(fluoroaryl)–P bond being protonated, and only trace amounts of the corresponding dibenzophosphole 8ca were formed (Scheme b, cf.…”

Straightforward Access to Multifunctional π‐Conjugated P‐Heterocycles Featuring an Internal Ylidic Bond**

“…[25] Interestingly, Xu et al reported that the Pd-catalysed intramolecular cyclization of related carbonyl-stabilized phosphonium ylides proceed through Ullman-type O-arylation. [26] With our phosphonium, the use of various Pd catalysts (Pd-(PPh 3 ) 4 , PdCl 2 (PPh 3 ) 2 , Pd(OAc) 2 etc.) did not change the rate of the reaction and only the λ 5 -phosphaacenaphthylene 5 a was formed in similar yields.…”

Straightforward access to multifunctional pi-conjugated P-heterocycles

“…[22] Interestingly, Xu et al reported that the Pdcatalysed intramolecular cyclization of related carbonyl-stabilized phosphonium ylides proceed through Ullman-type O-arylation. [23] With our phosphonium, the use of various Pd catalysts (Pd(PPh3)4, PdCl2(PPh3)2, Pd(OAc)2 etc) did not change the fate of the reaction and only the  5phosphaacenaphthylene 5a was formed in similar yields.…”