arenes are down in the polyarylmethane region and should be amenable to direct equilibrium measurement. Unfortunately, with CsCHA the higher polycyclic benzenoid hydrocarbons rapidly form radical anions such that we have been unable to accomplish such direct measurement.The present pK results may be related to the exchange rates of Ebel and Ritterbusch with lithium W-methylanilide at 150°.23 Their relative deuterium exchange rates for TPM, DPM, and 9-methylphenanthrene give a Brpnsted a of about 0.26 at 150°, a value that corresponds to ~0.37 at 25°if the effect is all in AH*.Hence, this reaction is much like that with LiCHA except that the anilide ion is a weaker base and higher temperatures are required for equivalent reactivities.
Mechanism of ítowí-Cinnamic Acid Dibromide to 8-Bromostyrene 2639 furic acid gave in the usual way a black crude phenol. Two treatments of this material in benzene solution with charcoal gave, in turn, a gray, waxy solid, which was sublimed to give 2,3-dimethyl-5-phenylphenol as colorless needles of m.p. 51-52°.
Ketone 4a was prepared from 2-cyclopentenone by photocycloaddition with 1,2-dichloroethylene, ketalization, dehalogenation, hydrogenation, bromination, dehydrobromination, and hydrolysis5 in an overall yield of 47%.6 7-Ketonorbornene, 6a, was identified by comparison of infrared and nmr spectra with those of authentic material.7•8 The synthesis of exo-6,7bisdeuteriobicyclo[3.2.0]hept-3-en-2-one, 4b, was accomplished as outlined above except that reduction with deuteriodiimide10 was substituted for the hydrogenation step. Irradiation of 4b as above gave 5,6bisdeuterio-7-ketonorbornene.Because of the simplicity of the nmr spectra of 7-ketonorbornenes,11 determination of the stereochemistry of the allylic rearrangement is simply a matter of measuring the ratio of endo and exo protons in the dideuterated product.12 The nmr spectrum of labeled 7-ketonorbornene obtained from irradiation of 4b exhibits signals at 1.90 and 1.13 corresponding to the exo and endo protons, respectively, on C-5 and C-6. The integrated area of the lower field signal is 2.5 times that of the upfield one, indicating that the photochemical isomerization, 4 6, proceeds with complete loss of stereochemistry at the migrating carbon.13In order to eliminate loss of stereochemical integrity in ketone 4 via rapid equilibration with diradical 5 followed by a slower concerted isomerization of 4 to 6 as a possible course of events, we determined the stereochemistry of product and of recovered starting ketone both after ca. 70 and 25% disappearance of starting ketone 4. The stereochemistry of product ketone, 6, as determined by the nmr analysis outlined above, was invariant with reaction progress. Starting(5) This sequence is a combination of methods first described by H. O'
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