Stereomutation of a 1,2,3-triketone: an example of an asymmetric reaction

Abstract

The 1,2,3-triketone PhC(Me)2COCOCOPh has been synthesized from mandelic acid in seven steps. Its proton magnetic resonance spectrum features a sharp six-proton methyl singlet at room temperature which broadens considerably at low temperatures but is not resolved into two peaks at 173 K. Similar dynamic behaviour is observed for the monoketone PhC(Me)2COPh. It is concluded that the barrier to interconversion of enantiomeric tricarbonyl helical conformations is significantly less than 7 kcal/mol. The rotation–rotation surface of the ketodialdehyde HCO—CO—CHO has been computed by the CNDO/2 method; the barrier to stereomutation of enantiomeric helical conformations of this tricarbonyl system is found to be 3.9 kcal/mol. The dynamics of this process are discussed in terms of a recently proposed definition of symmetric and asymmetric reactions.

The Chemistry of Vicinal Polycarbonyl Compounds

“…Conversion of β-dicarbonyl compounds to monobromo derivatives followed by replacement of bromine has received a new lease on life with the introduction of dimethyl sulfoxide as a mild reagent for replacing such activated bromine atoms by a carbonyl oxygen. These include 1,1-dimethyl-1,4-diphenylbutanetrione (15), used by Wolfe et al 25 in their investigation of possible helical conformations of the trione chain (see section VII.B), and a variety of simple triones (R 1 ) alkyl, aryl; R 2 ) alkyl, aryl, ester), prepared by Dahn and co-workers 24 for studies of base-catalyzed reactions of such compounds. These workers reported that the DMSO procedure gave better yields than the old procedure using N 2 O 3 , which has not been employed recently.…”

“…Both bond lengths and bond angles could be modified as compared with simple carbonyl compounds. In addition, the justifiable assumption 25 (see below) that rotational barriers about the intercarbonyl single bonds will be small means that chains of carbonyl groups can adopt a variety of conformations. Of particular interest is the possibility of helical (ergo chiral) conformations.…”

“…Conversion of β-dicarbonyl compounds to monobromo derivatives followed by replacement of bromine has received a new lease on life with the introduction of dimethyl sulfoxide as a mild reagent for replacing such activated bromine atoms by a carbonyl oxygen. These include 1,1-dimethyl-1,4-diphenylbutanetrione (15), used by Wolfe et al 25 in their investigation of possible helical conformations of the trione chain (see section VII.B), and a variety of simple triones (R 1 ) alkyl, aryl; R 2 ) alkyl, aryl, ester), prepared by Dahn and co-workers 24 for studies of base-catalyzed reactions of such compounds. These workers reported that the DMSO procedure gave better yields than the old procedure using N 2 O 3 , which has not been employed recently.Tatsugi and Izawa 26 have recently reported combining the bromination and DMSO oxidation steps by reaction of NBS in DMSO with 1,3-diketoindane at 80 °C under aspirator vacuum to form ninhydrin (4b) in high yield.The reaction of an R-bromo-R,β-unsaturated ketone in the ninhydrin series with DMSO has been reported by Heffner and Joullie ´27 to result in formation of benzo[f]ninhydrin (16).b.…”

Transition state determination by the X-method

“…The conformational surface was calculated using the CNINDO program (14). An actual analytic approximation of this E(o,,o,) surface by trigonometric functions is published elsewhere (13). The o, = o, = 0 conformation is defined by 1.…”

The photochemical reaction of 1,1-dicyano-3-phenylbut-1-ene. Simultaneous occurrence of pi-methane and di-pi-methane rearrangements

“…The final yield after extraction and distillation of the reaction mass was 67% (colourless oil, 146 °C/0.75 torr 18 . 2-Methyl-2-phenylpropanal used as a precursor in the synthesis of 3-DMDCN was obtained by a Grignard reaction between methyl mandelate and CH 3 I with pinacol formation (78%), followed by H 2 SO 4 /AcOH/I 2 treatment (yield ~60%), as described by Wolfe et al 19 The aldehyde was converted to 3-DMDCN with 61% yield by a . This compound was used as actinometer and for chromatographic and spectroscopic comparisons, as its photolysis rendered a single product.…”