Cyclopropanes. XIII. The Absolute Configuration of 1-Methyl-2,2-diphenylcyclopropane

Abstract

1-METHn-2,%DlPEENYLCYCLOPROPANE 4831It is the behavior in the acid solvents that is most striking. Catalysis by acid as found by Blomquist and FerrisI2 for t-butyl perbenzoate in several solvents containing trichloroacetic acid and as suggested by our experiment with heptafluorobutyric acid, is not apparent in most of the acids shown in Table IV. In acetic, ashloropropionic, propionic and n-butyric acids, the rates are not greatly different from those in chlorobenzene, and in the case of the last two are slightly lower. Although a-chloropropionic acid is a much stronger acid than acetic acid, the rate in it is smaller. Examination of the structures of these four acids suggested that their effects may be related to the number and strength of binding of the hydrogen atoms on the carbon atom alpha to the carboxylate group. This further suggested trying an acid with no hydrogen in the a-position, which explains the choice of a-chloroisobutyric acid.The great effect of the absence of hydrogen atoms on the a-carbon atom is shown by the more than fivefold increase in rate in a-chloroisobutyric acid above that in a-chloropropionic acid. When a mixture of 10 mole-per cent. of isobutyric acid and 90 mole-per cent. of a-chloroisobutyric acid was used as solvent with t-butyl permyristate a t llOo, the 105k value was 29.5 sec.-l, showing the inhibitory effect of the presence of the isobutyric acid.These results show that the acid catalysis expected of a carboxylic acid is diminished greatly if the acid has one or more hydrogen atoms on its cy-carbon atom. This stabilizing or inhibitory effect shows a dependence also upon the other atoms attached to the cy-carbon atom and in the (12) A. T. Blornquist and A. F. Ferris, J . A m . Chem. Soc., 73, 3412 (1951).case of propionic and butyric acids is great enough to render the net rate of decomposition of the perester lower than in pure chlorobenzene.Other evidence of combined inhibitory action and acid catalysis by carboxylic acids is found in the observations of Blomquist and Ferris12 with t-butyl perbenzoate. They found that the rate in acetic acid was higher than in aromatic solvents such as chlorobenzene a t the same temperature but that while addition of trichloroacetic acid to the ester in p-chlorotoluene had a marked catalytic effect, addition of dichloroacetic acid had practically no effect. An effect of the presence and the nature of the hydrogen atoms on the a-carbon of the acid is thus apparent in their work also.The exact nature of the action of carboxylic acids ;nust be determined by extensive further research and we do not wish to speculate upon it at present. No good clue to that nature is provided by the analysis of the products produced in n-butyric acid (Table VII) since that analysis is not sufficiently different from the one obtained for the decomposition in chlorobenzene. On the other hand, the effects of the acids on the AH* and AS* values (Table VI) do not fit well with the correlations found for peresters undergoing simple or "concerted" cleavage free of radi...

Organocatalytic Asymmetric Alkylation of Aldehydes by SN1‐Type Reaction of Alcohols

“…The absolute configuration of the products derived from alcohol 1 was established by correlation to known derivatives obtained by using a methodology reported by Paras and MacMillan18, 19 (see the Supporting Information). The absolute configuration of the products derived from alcohol 5 was assigned by comparison of the elution order of the products from a chiral phase HPLC column to those reported in the literature 20.…”

Metal catalyst-free substitution of allylic and propargylic phosphates with diarylmethyl anions

“…The substitution proceeded at À15 1C and completed in 1 h to afford the retention product (R)-4 in 83% yield with 499% a regioselectivity (rs) and 94% enantiospecificity (es) 7 as determined by 1 H NMR and chiral HPLC, respectively. The absolute configuration of (R)-4 was determined by oxidative degradation to the known acid, (R)-(Ph 2 CH)MeCHCO 2 H (5) 8 (NaIO 4 , RuCl 3 Á nH 2 O). Owing to the achievement of the excellent result, the original protocol using Xantphos in DME was not examined.…”

Organocatalytic Asymmetric Alkylation of Aldehydes by SN1‐Type Reaction of Alcohols

“…Performing the reaction at low temperature (À25 8C, Table 2, entry 15) provided better control of the stereoselection at the expense of the yield. The absolute configuration of the products derived from alcohol 1 was established by correlation to known derivatives obtained by using a methodology reported by Paras and MacMillan [18,19] (see the Supporting Information). The absolute configuration of the products derived from alcohol 5 was assigned by comparison of the elution order of the products from a chiral phase HPLC column to those reported in the literature.…”