Phosphites with aroyl chlorides

The palladium-catalyzed system can be extended to the acylation of siloxycyclopropanes with aroyl chloride/carbon monoxide or aryl triflate/carbon monoxide, which gives 1,4-diketones. Contrary to the case of doubly oxygen-substituted cyclopropanes vide infra), the acylation of 1-siloxycyclopropanes is restricted to aroyl chlorides and is not applicable to aliphatic or a, -unsaturated acyl chlorides. For the reactions with aryl triflates, tetrakis(triphenylphos-phane)palladium(O) is used as catalyst, while the reactions with aroyl chlorides employ bis(triphenylphosphane)palladium(II) chloride and ( / -allyl)chloropalladium dimer/triphenyl phosphite as catalysts. In these reactions, aroylpalladium(II) species may undergo ring opening of the siloxycyclopropanes. 

General procedure for the preparation of dialkyl aroylphosphonates 279 The aroyl chloride (0.03 mole) is treated under nitrogen dropwise with the trialkyl phosphite (0.04 mole) at such a rate that the internal temperature does not exceed 35°. The resulting mixture is fractionated in a vacuum. As example, dimethyl benzoylphosphonate, b.p. 146°/2.5 mm, is obtained in 81 % yield from benzoyl chloride and trimethyl phosphite. 

A synthesis of racemic fmoc-protected 4-phosphonomethylphenylalanine starts with the Arbuzov preparation of (257) (R = Me or Bu ) standard modifications to the aryl methyl group lead to the desired (258). Two procedures have been adopted for the preparation of the N-ivaoc or iV-boc derivatives of the difluoro derivative (259). In the first, triethyl phosphite and 4-(bromomethyl)benzoyl bromide and treatment of the resultant aroyl phosphonate with the DAST reagent yields (262) this reacts with the carbanion from (263) to give (264) hydrogenation of which (with PdCla) affords (260), then converted into its N-fmoc derivative and de-esterified with MeaSil. In the second procedure, triethyl phosphite and 4-iodobenzoyl chloride, followed by DAST reagent, yielded diethyl [difluoro(4-iodophenyl)methyl]phosphonate which was caused to react... 

On the other hand, when the Arbuzov reactions of aroyl (/ -nitrobenzoyl, benzoyl, p-chlorobenzoyl or / -toluoyl) chlorides were carried out in the presence of proton sources (i.e. excess of a carboxylic acid), phosphate phosphonates were obtained as shown in equation 19 The formation of these resulted from protonation of the initially formed carbanion, to form a phosphonate trialkoxyphosphonium ion, followed by nucleophilic dealkylation of the trialkoxyphosphonium moiety. Indeed, the formation of carboxylate esters as additional products was noted in these reactions. The type of products shown in this reaction show characteristic resonances in the NMR spectrum in the ranges 0.8-1.25 and 16-17 ppm with /pp = 29 Hz. Analogous results were observed in the reaction of 2-pyridoyl chloride with triethyl phosphite. ... 

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