Kazimir I. Pashkevich

Fluorinated 1,3-diketones, 2-trifluoroacetyl phenols and their derivatives: versatile reactants in phosphorus chemistry

Abstract The role of fluorinated β-diketones, their tautomers (keto–enols) and their derivatives as reagents towards λ 3 P compounds is reviewed, including 2-trifluoroacetyl phenols, possessing formally a keto–enol system, and their derivatives. In an ‘insertion’ reaction phosphine and the keto–enol tautomers of 1,1,1,5,5,5-hexafluoro- and 1,1,1-trifluoropentan-2,4-dione furnished primary ( S ) or ( R ) α-hydroxy phosphines, whose enol functions probably isomerized the corresponding keto compounds. Further addition and isomerisation furnished 1,3α,5,7β-tetrakis(trifluoromethyl)-2-phospha-6-oxa-9-oxabicyclo[3.3.1]-nonan-3β,7α-diol and 1,7-trifluoromethyl-3,5-methyl-2,4,8-trioxa-6-phophaadamantane, exclusively one diastereomer in each case. The main mechanistic feature of these reactions is a consecutive diastereoselective hemiketal cyclization. 1,1,1,5,5,5-Hexafluoro- and 1,1,1-trifluoropentan-2,4-dione, as well as 2-trifluoroacetyl phenol and its imino derivatives reacted diastereospecifically with phosphonous acid dichlorides, RPCl 2 to give in a concerted mechanism thermally stable tricyclic λ 5 σ 5 P phosphoranes containing two five-membered rings and one six-membered ring. Surprisingly, the two CF 3 groups bonded to an sp 3 -hybridized carbon were in a cisoid arrangement having closest non-bonding F⋯F distances of 301.4 or 273.5 pm. These findings reflect the ‘through space’ Fue5f8F coupling constants of the tricyclic phosphoranes ( J FF =4.0–7.0 Hz), in solution. 4,4,4-Trifluoro-3-hydroxy-1-phenyl-butan-1-one and methyl or phenyl phosphonous acid dichlorides gave similar tricyclic phosphoranes decomposing at ambient temperature to furnish 1,2λ 5 σ 4 -oxaphospholanes and ( E )-1,1,1-trifluoro-4-phenyl-but-2-en-4-one. Dialkylphosphites and 1,1,1,5,5,5-hexafluoropentan-2,4-dione reacted to give either the ( Z )-enol phosphonates or the respective γ-ketophosphonates from which in two cases four diastereomeric 2-oxo-2,5-dialkoxy-3,5-bis(trifluoromethyl)-3-hydroxy-1,2λ 5 σ 4 -oxa-phospholanes were obtained. 2-Trifluoroacetyl cyclohexanone, 4,4,4-trifluoro-3-trimethylsiloxy-1-phenylbutan-1-one, 1-benzoyl-2-trifluormethyloxirane, 1-benzoyl-2-trifluoro-methylaziridine, 2-trifluoroacetyl-1-trimethylsiloxybenzene and (trifluoroacetyl-1-phenyl) diethyl phosphate reacted with tris(trimethylsilyl) phosphite to give functionalized α-trimethylsiloxy phosphonates, which could easily be transferred into the respective phosphonic acids. In the case of an oxirane and an aziridine ketone no ring cleavage was observed. For 1,1′-(2-hydroxy-5-methyl- m -phenylene)-bis-ethanone and 1,1′-(2-trimethylsiloxy-5-methyl- m -phenylene)-bis-ethanone benzoxaphospholanes were obtained. Trialkyl phosphites and 1,1,1,5,5,5-hexafluoropentan-2,4-dione furnished cyclic phosphoranes containing the 3-hydroxy-3,5-bis(trifluoromethyl)-1,2λ 5 σ 5 -oxaphospholene structural element, stable at ambient temperature only in the case of one cyclic phosphite precursor. ( E )-1,1,1-Trifluoro-4-phenyl-but-2-en-4-one and trimethylphosphite reacted to form 1,2λ 5 σ 5 -oxaphosphol-4-ene as the sole product. Results similar to the reaction of 1,1′-(2-hydroxy-5-methyl- m -phenylene)-bis-ethanone with diethyltrimethylsilylphosphite were obtained for trimethylphosphite and 2-trifluoroacetyl phenol where a deoxygenated phosphorane was found, easily hydrolyzed to give the respective phosphonic acid. With dialkylisocyanato phosphites and the keto components, 1,1,1,5,5,5-hexafluoro- and 1,1,1-trifluoropentan-2,4-dione, 4,4,4-trifluoro-1-phenyl-1,3-butandione, 2-trifluoroacetyl cyclohexanone, 2-trifluoroacetyl phenol and 1,1′-(2-hydroxy-5-methyl- m -phenylene)-bis-ethanone reacted in a ‘double’ cycloaddition to form bicyclic phosphoranes containing the 4,8-dioxa-2-aza-1λ 5 σ 5 -phosphabicyclo[3.3.0]-oct-6-en-3-one ring system; for the imino derivatives of 2-trifluoroacetyl phenol a corresponding 8-oxa-2,4-diaza- system was generated. For ( E )-1,1,1,5,5,5-hexafluoro-4-trimethylsiloxy-3-penten-2-one however, a cyclic spiroimino phosphorane was obtained which underwent a [2+2] cyclodimerization to form a diazadiphosphetidine. Dimethylpropynyl phosphonite and 1,1,1,5,5,5-hexafluoropentan-2,4-dione yielded diastereoselectively a bisphosphorane, namely 1,4-bis(trifluoromethyl)-3,6-dioxa-2,2,7,7-tetramethoxy-2,7-di(1-propynyl)-2,7-diphosphabicyclo[2.2.1] heptane. When trimethylsilanyl–phosphenimidous acid bis-trimethylsilanyl–amide, Me 3 SiNue605PN(SiMe 3 ) 2 , was allowed to react with 1,1,1,5,5,5-hexafluoro- and 1,1,1-trifluoropentan-2,4-dione, ( E )-1,1,1,5,5,5-hexafluoro-4-trimethylsiloxy-3-penten-2-one, 2-trifluoroacetyl cyclopentanone, 2-trifluoroacetyl phenol and its imino derivatives, 2-imino-1,2λ 5 σ 4 -oxaphospholenes were found containing two diastereomers in each case, which added hexafluoroacetone across the Pue605N bond to give 1,3,2λ 5 σ 5 -oxazaphosphetanes.

(E)-1,1,1-trifluoro-4-phenyl-but-2-ene-4-one and trimethyl phosphite

Abstract The interaction of (E)-1,1,1-trifluoro-4-phenyl-but-2-ene-4-one (1) with trimethyl phosphite affords in a [4xa0+xa01] cycloaddition the 1,2λ5-oxaphospholene 2 as a sole product which upon hydrolysis is transformed into the fluoroalkyl containing γ-ketophosphonate 4. When the reaction is carried out in the presence of small mounts of water, in addition to 2 as a main product, the phosphoric acid ester 6 of the enolic dimer of ketone 1 is also formed. The molecular structure of compound 6 (monoclinic P 2(1)/c with axa0=xa02088.60(2), bxa0=xa01403.1(3), cxa0=xa01613.8(1)xa0pm, αxa0=xa090, βxa0=xa0100.97(1), γxa0=xa090°, Zxa0=xa08) was determined, indicating two independent molecules with (RR) and (SS) configuration and disordered CF3 groups.

Trifluoromethylated 1,2λ5σ4-oxaphospholanes via λ5σ5P tricyclic phosphoranes from 4,4,4-trifluoro-3-hydroxy-1-phenylbutane-1-one and dichlorophosphines. Molecular structure of a trapped phosphonite

Abstract Reacting 4,4,4-trifluoro-3-hydroxy-1-phenylbutane-1-one (1) with the dichlorophosphines RPCl 2 ( 2a , R = Me; 2b , R = Ph) gave the phosphonites 3a and 3b , which, in the case of 3a , was trapped using hexaHuoroacetone to furnish the 1,3,2λ 5 σ 5 -dioxaphospholane 4a . In a concerted mechanism, compounds 3a and 3b rearranged forming the thermally unstable tricyclic diastereoisomeric phosphoranes 5a and 5b . After splitting off 1,1,1-trifluoro-4-phenyl-2-butene-4-one (6) the diastereoisomeric 1,2λ 5 σ 4 -oxaphospholanes 7a and 7b were obtained. The molecular structure of 4a (triclinic, P , a =1020.3(1) pm, b =1239.0(1) pm, c =1298.7(2) pm, a = 85.55(1) °, 0 = 70.10(1) °, γ=79.85(1) °) was determined.

The electrophilic thionation and chlorination of polyfluorinated α-Keto esters

Abstract The methyl ester of trifluoropyruvic acid reacts with phosphorus pentachloride at the keto carbonyl as well as at the ester carbonyl group. The reaction of polyfluorinated α-keto esters with Davys reagent occurs regioselectively at the keto carbonyl and is accompanied by reduction and thiomethylation.

Unexpected reaction of 1,1,1,10,10,10-hexafluorodecane-2,4,7,9-tetrone with methyl trifluoroacetate

Hexane-2,5-dione or 1,1,1,10,10,10-hexafluorodecane-2,4,7,9-tetrone react with methyl trifluoroacetate in the presence of LiH to give, upon treatment with diluted acid, 6-hydroxy-9-oxo-2,4,10-tris(trifluoromethyl)-3,11,12-trioxatetracyclo[5,2,1,02,6,04,10]dodecane. The structure of this compound was determined by X-ray diffraction study.

Effective fluoroalkylation of aldehydes by σ-perfluoroalkyl-iron compounds

Abstract Organoiron compounds with σ-perfluoroalkyl-iron bonds are well-known and common compounds convenient to prepare and handle. However, their application in organic synthesis was restricted to the introduction of fluoroalkyl group only into electron rich organic molecules such as arenes and thiols [I.I. Gerus, Yu.L. Yagupolskii and L.M. Yagupolskii, J. Org. Chem. (Russ. ed.), 21 (1985) 1852; C.G. Krespan, J. Fluor. Chem., 40 (1988) 129]. In this work we have succeeded in the use of the perfluoroalkyltetracarbonyliron iodides for the nucleophilic fluoroalkylation of aldehydes: The reaction is rapid (∼ 1 h), easy to carry out and does not require an inert atmosphere. From the synthetic point of view it is promising since the starting organoiron compounds are readily prepared from fluoroalkyl iodides and solid substances stable in air.

An efficient synthesis of alkylfluoroalkylketones

Abstract Interaction of fluoroacyl chlorides with lithium tetraalkylaluminates II prepared by the hydroalumination of alkenes I results in fluorinated ketones III with yields of 65–70%. R F = CF 3 , H(CF 2 ) 2 , C 4 F 9 , C 6 F 13 R 1 = C 3 H 7 , C 4 H 9 , C 6 H 13 , C 7 H 15 The reaction is simple and does not require an argon atmosphere, as is needed for most reactions of organoaluminum compounds.

Regiospecifity reactions of the esters of fluorinated α- and β-ketoacids with nucleophilic reagents

Abstract The data about regiospecificity of reaction of the fluoroalkylcontaining esters of α-ketoacids (I) and β- ketoacids (II) with HO-, HS- and HN nucleophiles are discussed. This regiospecificity is conditioned by two reactional centers availability. There are ester and carbonyl groups. Dependence between reactivity of fluorinated ketoester and mutual disposition of both reactional center (next (I) or isolated over -CH 2 -, -CHCl-, -CBr 2 - (II)) is under consideration. Peculiarity of the process is conditioned by the structure of fluoroalkyl substituent R F for (I) and for (II), by presense of halogen atom in α-position for (II) and by enolisation of (II) if x = y = H and x = H, y = Cl.

Syntheis, structure and reactivity of fluorinated α,β-unsaturated and α,β-epoxy ketones

Abstract New polyfluorinated α,β-unsaturated ketones (I) have been prepared by a condensation of fluoroalkyl aldehydes with methylketones or fluorinated β-diketones. The heminal arrangement of Cue5f8C double bond and fluoroalkyl substituent in (I) is shown to be always formed irrespective of the structure of fluorinated group in the aldehydes and the β-diketones studied. Trans-s-cis form is determined by the methods of vibrational and NMR spectroscopy to be preferred one for (I). Addition of O-, N-, C- nucleophilic species is directed to the β-carbon atom of (I), saturated β-substituted β-fluoroalkyl ketones being obtained. New polyfluorinated α,β-epoxy ketones (II) have been approached to by an epoxidation of (II) with H 2 O 2 in alkaline medium. The structure of (II) is discussed on the basis of IR and NMR spectroscopy. The interaction of compounds (I) and (II) with 2,4- -bis (4′-methoxyphenyl)-2,4-dithioxo-1,3,2,4-dithiadiphosphetane proceeding with the formation of some new fluorosuphur compounds is considered.