Reaction of phospholes with acids; [1,5] proton shifts in 1H-λ⁵-phospholes

Abstract

Addition to phospholes of gaseous HCI at -90 "C or of an excess of trifluoromethanesulphonic acid at -70 "C, results in P-protonation. The triflate solutions are stable up to room temperature, but the 1 Hphospholium chlorides form P V adducts at -70 "C, which rapidly rearrange by a [1,5]sigmatropic Hshift. The observed product is a 1 -chloro-2,5-dihydrophospholium chloride. Addition of a chloride ion source to the triflates produces the same result. Unprotonated 3,4-dimethyl-1 -phenyl phosphole was found to react at a double bond of its 1H-phospholium ion, forming a crystalline 1,3'-biphospholium dimer.Considerable evidence has accumulated recently to support the concept that among phosphole derivatives [ 1,5] sigmatropic shifts of P-substituents to a ring a-carbon atom are common. Such rearrangements have been encountered when the phosphorus has co-ordination states of three (H' and phenyl migrations), four (phenyl migration 2), and five (phenyl and alkoxy 4 * 5 migration). Migration appears to be faster for H than for phenyl, with alkoxy slower than either; also Pv derivatives rearrange faster than PIv and PI''. A combination of these two effects suggests that rearrangement should be exceptionally fast when H is a substituent on phosphorus(v), as in a h5-phosphole * This appears to be a new observation for a phosphine salt. Other examples have been encountered in related work and will be reported elsewhere (L. D. Quin and S. E. Belmont).1969, 91, 3308.

The organic chemistry of phospholes

“…1W-Phospholes 1. Nucleophilic Properties of Phosphorus The reaction of phospholes with acids was understood only very recently. 124 It leads to phospholene derivatives that formally result from the protonation of the phosphole ring at carbon. Two such reactions have been described.…”

Revisiting the 7‐Phospanorbornene Family: New P‐Alkyl Derivatives

“…C 2015 Wiley Periodicals, Inc. justified by semiempirical calculations [6]. The results of Quin, Mathey, and other authors revealed the importance of the 7-phosphanorbornene derivatives in fragmentation-related phosphorylation reactions [7][8][9], complexations [10][11][12], and in re-functionalizations [13][14][15][16] including deoxygenations [17][18][19]. The Bayer-Villiger oxidation of 7-phosphanorbornenes leads to valuable oxaphosphabicyclo [2.2.2]octene derivatives that may be useful in fragmentation-related phosphorylations [20][21][22][23][24][25].…”

Phosphorus Heterocycles

“…The second method relies on the dehydrohalogenation of diene-dihalophosphine cycloadducts [24]. The postulated mechanism is depicted in Scheme 23.2 [25].…”

“…The P-H þ salts are only stable when the counterion (e.g., TaCl 6 À ) does not display any coordinating ability [39]. Otherwise they evolve to give phospholene oxides via a pentacoordinate intermediate and a [1,5]-shift of H [25]. The oxides tend to dimerize via a [4 þ 2] Diels-Alder reaction and display a limited life time at room temperature [40] except when heavily substituted on the ring.…”

“…But the most spectacular applications of heterocyclic phosphines are in the field of enantioselective catalysis. To cite only the best known examples, the phospholane-based DuPHOS (24) [220], phosphetane-based FerroTANE (25) [221,222], phosphanorbornane-based Penn-Phos (26) [223] and the phosphanorbornadiene-based BIPNOR (27) Phosphorus heterocycles are also showing some promise in the field of molecular materials. A low-molecular weight polymer (up to 7800) has been obtained by cationic polymerization of a phosphirane (Scheme 23.81) [225].…”