Philip J. Sellars

3,3,3-Trifluoropropan-1-ol and 3,3,3-trifluoropropanal

Abstract Acetoxymercuration of 3,3,3-trifluoropropene leads to 1-acetoxy-3,3,3- trifluoropropene which is hydrolysed to 3,3,3-trifluoropropanol, oxidation of which affords 3,3,3-trifluoropropanal.

Masking the carboxy group as a 2,6,7-trioxabicyclo[2.2.2]octane: application to the synthesis of alkylcobaloximes containing ester and carboxy groups

The hydrolytic stability of 2,6,7-trioxabicyclo-[2.2.2]octanes towards aqueous acid is intermediate between that of 1,1,1-triethoxyethane and 1-methyl-2,8,9-trioxa-adamantane; a synthetic application of this trioxabicyclo-octane group as a masked carboxy function is described.

A model system based on photodecompositions of alkylcobaloximes for the conversion of 1,2-diols to aldehydes catalysed by diol dehydrase

Attempts to model the conversion of 1,2-diols to aldehydes catalysed by the adenosylcobalamin-dependent enzyme diol dehydrase utilising the photohomolysis of alkylcobaloximes, have been carried out in two ways. First, the alkyl radical released from such photolysis has been shown to convert ethane-1,2-diol to CH3CHO at pH 2 with an efficiency of ca. 10%. Second, photolysis of several compounds of the type HOCH2CHOH[CH2]n-Co(dmgH)2(C5H5N) yields products (when n= 3 or 4) suggestive of the sequence: (a) photohomolysis followed by (b) an intramolecular 1,5-hydrogen shift (n= 3 or 4) or 1,6-hydrogen shift (n= 4) to produce a 1,2-dihydroxyalkyl radical which in turn undergoes (c) further transformations, including either an acid-catalysed 1,2-hydroxy shift [to give a 1-(dihydroxymethyl)alkyl radical], or acid-catalysed dehydration to R1ĊHCOR2(R1= Prn, R2= H, R1= H, R2= Bun, or R1= Bun, R2= H), finally yielding R1CH2COR2. When n= 3, the exclusive carbonylcontaining product from the dihydroxyalkyl group is pentanal (via a 1,5-hydrogen shift). These results enable us to counter claims that radical chemistry cannot simulate the diol dehydrase reactions, and to provide a critique of the present discussion of models for adenosylcobalamin-dependent enzymatic reactions.

Model experiments relevant to the mechanism of adenosylcobalamin-dependent diol dehydrase: further investigations of isomerisations of dihydroxyalkyl radicals

Anaerobic photolysis of 4,5-dihydroxypentyl(pyridine)cobaloxime in 0.1M acetic acid (pH 3) gives ca. 10% of pentanal, whereas 1,1,5,5-tetradeuterio-4,5-dihydroxypentyl(pyridine)cobaloxime affords 0.6% of 1,5,5,5-tetradeuteriopentanal. Under similar conditions, 5-deuterio-5,6-dihydroxyhexyl(pyridine)cobaloxime gives ca. 1% of 6-deuteriohexan-2-one and 4% of 2-deuteriohexanal, in contrast to 5,6-dihydroxyhexyl(pyridine)cobaloxime which affords 16% of hexan-2-one and 4% of hexanal. These results support a mechanism for the photocon-version of dihydroxyalkylcobaloximes into aldehydes or ketones at pH 3, in which light-induced homolysis of the Co–C σ-bond to give a dihydroxyalkyl radical is followed by a 1,5-hydrogen shift. The resulting isomeric dihydroxyalkyl radical, possessing a hydroxy-group at the radical centre, undergoes an acid-catalysed transformation to aldehyde or ketone. With the deuteriated cobaloximes the 1,5-H shift is impeded by a primary isotope effect (kH/kDca. 20). Anaerobic photolysis of 4,5-dihydroxycyclo-octyl(pyridine)cobaloxime at pH 3 yields ca. 40% of cyclo-octanone. This reaction owes its efficiency to a favourable transannular 1,5-H shift which converts the 4,5-dihydroxycyclo-octyl radical into the 1,2-dihydroxycyclo-octyl radical. The relevance of the above reactions to adenosylcobalamin-dependent reactions catalysed by diol dehydrase is discussed.

Resolution of racemic epoxides on g.l.c. columns containing optically active lanthanoid complexes

Racemic epoxypropane and 1,2-epoxybutane are resolved on a 2 m g.l.c. column containing the lanthanoid complex (1, R = CF3. M = Eu or Pr) in the stationary phase; (S)-epoxypropane is eluted more slowly than the (R)-isomer.

Preparation of N-arylmethylglycinato-bis-(ethane-1,2-diamine)cobalt(III) complexes. Comparison of their exchange reactions at pD 9.7

Abstract The preparation and characterisation of N-arylmethylglycinato bis-(ethane-1,2-diamine)cobalt(III) complexes, where aryl = phenyl (1a) 2-methylphenyl (1b) and naphthyl (1c), are described. In contrast to (1a), exchange of the diastereotopic glycinate methylene protons in (1b) and (1c) in borax buffer (pD 9.7) is shown to proceed non-stereoselectively.

Study of reactions between alkyl(pyridine)cobaloximes and trifluoroacetic acid; formation and crystal structure of cis-bis(butane-2,3 dione dioxime)bis(trifluoroacetoxy)cobalt(II)

The reactions between several alkyl(pyridine)cobaloximes [CoR(Hdmg)2(py)][R = Me, CH2Cl, CHCl2, Et, Pri, Bun, CH2CH2CHCH2, or CH2CHMeCHCH2, (1a)–(1h) respectively; py = pyridine; Hdmg = monoanion of dimethylglyoxime] and trifluoroacetic acid in deuteriochloroform have been monitored by 1H n.m.r. spectroscopy. This technique indicates that addition of trifluoroacetic acid to an alkyl(pyridine)cobaloxime initially causes reversible protonation without loss of pyridine, then a second protonation occurs leading to the loss of pyridine as pyridinium trifluoroacetate. With excess of trifluoroacetic acid, the alkylcobaloximes lose their alkyl group as RH [e.g. propane from (1e)] and slowly deposit a red crystalline solid, identified as the title complex (4) by analysis of its crystal structure. Crystals of (4) are triclinic, space group P, with a= 10.068(3), b= 10.716(5), c= 13.030(3)A, α= 100.15(3), β= 116.76(3), γ= 88.97(3)°, and Z= 2. 1 873 Reflections collected at –80 °C by a four-circle diffractometer were refined to R= 0.053. The Co–O distances are 2.069(2) and 2.057(2)A; and Co–N are 2.126(3), 2.138(2), 2.139(3), and 2.149(3)A.

A mononuclear cis-cobaloxime: X-ray crystal structure of di-trifluoroacetoxybis(butane-2,3-dione dioxime)cobalt(II)

Treatment of several alkyl(pyridine)cobaloximes with an excess of trifluoroacetic acid in chloroform gives the crystalline cis-cobaloxime(II) complex: di-trifluoroacetoxybis(butane-2,3-dione dioxime)cobalt(II) identified by single crystal analysis.

Rearrangements of cyclopropylmethyl and but-3-enyl cobaloximes

[1-13C]-1-Cyclopropylmethyl(pyridine)cobaloxime (1b) rearranges (in CDCl3 at 310 K) to [4-13C]-but-3-enyl(pyridine)cobaloxime (2b); 1-methylbut-3-enyl(pyridine)cobaloxime (3) rearranges to 2-methylbut-3-enyl(pyridine)cobaloxime (4) under the catalytic influence of trifluoroacetic acid in CDCl3.

Investigation by deuterium-labelling of the isomerisation of dihydroxyalkyl radicals formed upon photolysis of cobaloxime complexes

Anaerobic photolysis of 5-deuterio-4,5-dihydrooxyhexyl(pyridine)cobaloxime at pH 3 gives 2-deuteriohexanal and probably 6-deuteriohexan-2-one.