Mechanistic and synthetic aspects of the reaction of γ-halogeno-α,β-unsaturated ketones and esters with simple trialkyl phosphites

Abstract

Phosphorylation of different gamma-halogeno-alpha,beta-unsaturated ketones, ketoesters and diesters 11a-h with simple trialkyl phosphites gives 1,3-dienylphosphates 14, cyclopropylphosphonates 15, ketovinylphosphonates 17 and other products depending on the nature and number of activating groups and halogen atoms in the substrate. Most likely the reaction proceeds via oxaphospholene 23 which is in equilibrium with pseudorotamer 24 and an open, dipolar form 22. Dipolar form 33 is a likely intermediate when two activating groups are present.

Reactions of β-alkoxyvinyl trihalogenomethyl ketones with triethyl phosphite

“…Instead of published results (the reaction temperature was 80-140 8C) [21] in our case the enones 13 react with triethyl phosphite at room temperature for several days in ether solution and corresponding dienyl phosphates 14 and 18 are formed in moderate yields (based on the 19 F and 31 P NMR spectra of the reaction mixtures) as a result of Perkow reaction (Schemes 8 and 11; Table 1, entries 9-11). In the case of the reaction between enone 13a and triethyl phosphite the phosphate 14 was formed which structure is very similar to non-fluorinated analogs: the chemical shift of the proton at the position 2 in the 14 (doublet at 6.08 ppm, 4 J HP = 2.0 Hz) is similar to Z-isomer of non-fluorinated analog (doublet at 6.02 ppm, 4 J HP = 1.0 Hz) [21].…”

“…Recently Polish scientists [21] supposed the mechanism of a reaction between ghalogeno-a,b-unsaturated ketones and trialkyl phosphites which ran through initial formation of oxaphospholene intermediate. We believe that in our case a similar cyclic intermediate 10 is also formed primarily (Scheme 6).…”

“…In the case of the reaction between enone 13a and triethyl phosphite the phosphate 14 was formed which structure is very similar to non-fluorinated analogs: the chemical shift of the proton at the position 2 in the 14 (doublet at 6.08 ppm, 4 J HP = 2.0 Hz) is similar to Z-isomer of non-fluorinated analog (doublet at 6.02 ppm, 4 J HP = 1.0 Hz) [21]. The diethyl phosphate group demonstrates a characteristic signal in the 31 P NMR spectra as multiplet at about À3.09 ppm, and a characteristic signal of trifluoromethyl group bonded to C C double bond is observed in the 19 F NMR spectra: singlet at À71.24 ppm.…”

“…This assumption based on stereochemical evaluation of similar products of Perkow rearrangement and arose from proposed mechanism of the reaction which runs through initial formation of oxaphospholene intermediate [21]. We believe, in the case of vinylogous Perkow reaction between enone 13a and triethyl phosphite the same cyclic intermediate 15 is formed primarily also (Scheme 9).…”

“…As it was mentioned above W. Waszkuć and T. Janecki demonstrated that the structure of products (dienyl phosphates or phosphonates-results of Perkow or Arbuzov reactions, correspondingly) depends on the nature of g-halogenoketones [21]. Recently, we published simple and useful synthetic route to g-bromo-b-alkoxy-a,b-unsaturated ketones 13 by bromination enones 12 [22] (Scheme 7) and it was interesting to check on the regioselectivity of a phosphorylation of the enones 13b,c bearing as g-bromo-so a-chloro-substituents which both can be involved in Perkow reaction.…”