COMMUNICATIONS TO THE EDITOR
3914
lated benzylboron dichloride from these reactions or from the pyrolysis of the chloroborate. In the absence of details of their work we cannot account for the difference in products, but the isolation of 84.570 tropeniuin and recovered cycloheptatriene in our cyclohexane reaction indicates that aromatization is not a major factor under our conditions.
VOl. 83 !IXN/ CHzR
CHiR
&!\ N'
CH3
\
I1
&\CH3
I11
When R = CBH6the proton resonance spectrum in CDCla has a sharp methyl signal a t 2.37 ppm., DEPARTMENT OF CHEMISTRY KENNETH M. HARMON complex aromatics a t -7 ppni., and a t 16.5 pptn. the HARVEY MUDDCOLLEGE ANN B. HARMON broad signal from the acidic proton (the acidic proE. CUMMINCS'~ CLAREMONT, CALIFORNIA FRANK ton in acetylacetone enol is a t 15.3 ppm. in CeH12a). RECEIVED JUNE 19, 1961 At 4.67 ppm. there is a field invariant doublet which collapses to a singlet upon deuteration of the A NUCLEAR MAGNETIC RESONANCE STUDY OF acidic proton and is thus ascribable to the benzyl KETO-ENOL EQUILIBRIA IN SCHIFF BASES. I1 methylene group split by N-H with J = 4.8 cps. When R = H the spectrum in either pyridine or Sir : A recent paper' presented evidence from proton CDClt is analogous to that of the benzyl base. I n magnetic resonance that bases derived from the 2: 1 CDC13 the methyl doublet is a t 3.08 ppiu. with J = condensation of a &diketone and a diamine are 4.4 cps. In both compounds the stability of the present in solution to an extent >95Y0 in the keta- keto-amine form with its chelated hydrogen-bonded mine form with only a small dependence of the equi- ring (inferred in both cases from the presence of a librium on solvent. The -NH-R structure was in- highly unshielded proton) is suflicient to destroy ferred from spin-spin splitting of the R methylene the aromatic structure of one of the naphthalene protons ( J = 6 cps.) by N-H. This study now has rings. These results present some of the most direct been extended to bases derived from other mono- physical evidence for such an effect. Previously, amines and @-diketonesin order to explore further similar tautomerism in certain arylazonaphthols the apparently high stability of the ketamine over had been inferred from ultraviolet and infrared ~ p e c t r a . ~ J .As ~ expected, salicylalbenzylamine the enol-imine tautomer. shows an unsplit methylene signal a t 4.77 ppm. in Bases formed from monoamines and simple @diketones such as acetylacetone give rise to proton CDCls. Preliminary studies of similar bases derived from resonance spectra similar to those derived from diamines. When K = H , CHI, G H s the com- 2-hydroxy-1-naphthone and 2-hydroxy-1-naphpounds in CDCla or CCld solution exist in the keta- thaldehyde indicate that the phenol-imine form predominates. When R = H in the former the mine form I as indicated by the vinyl signal a t -4.9 ppni.' and the splitting of the methyl or methylene N-methyl signal is a sharp singlet a t 3.21 ppm. in protons into a doublet with J ss 5-6 cps. CDC13. The benzyl base of the aldehyde exhibits a t 4.73 ppm. in CDCll a broadened methylene resonance which persists in CC14 and pyridine. These and other bases derived from o-hydroxynaphthaldehydes and o-hydroxylnaphthones are presently under investigation and detailed results will be reported in the future. CH3 CHZR Spectra were taken on a Varian IIK-60 (at 01) I or 1-5.1Mc./sec.) or A-BO spectrometer using tetraThe benzyl base of dibenzoylmetliane behaves sitni- tnethylsilaue as an internal zero of reference. larly. No other signals attributable to the N-sub- Rases were formed from the carbonyl compound stituent were observable (concn. -0.4 M ) so that and amine by standard procedures. Compounds structure I is present to an extent >950/0. There were characterized by melting point or in the case of is no apparent solvent effect upon the equilibrium new compounds by elemental analysis. Financial (CDC13, C6He, pyridine). support from the National Science Foundation is These results, together with corroborative in- acknowledged. frared studies on the above and related compounds,2 (3) L. W. Reeve% Con. J . Chcm., 96, 1351 (1957). offer further evidence of the greater stability of the (4) A. Burawoy and A . R . Thompson, J . Chcm. SOC.,1443 (1963) (5) E. Sawicki, J . Org. Chem., 99, 743 (1957). ketamine form in aliphatic compounds as compared ( 8 ) K . J. Morgan, J . Chcm. SOC.,2151 (l96l), and references therein. to either the ketimine or enol-imine tautomers. OF CHEMISTRY Accordingly, a search was made for other systems in DEPARTMENT UNIVERSITY G. 0. DUDEK which an alternate tautomer would be of compa- HARVARD R. H. HOLM CAMBRIDGE 38, MASS. rable stability, RECEIVED AUGUST16, 1961 Derivatives of o-hydroxynaphthones were investigated. The tautomers JI and 111 are possible STRUCTURE OF a-LUMICOLCHICINE-SOME for the base derived from I-hydroxy-2-naplithone THE EXAMPLES OF DIAMAGNETIC SHIELDING BY THE and a monoamine. CARBON-OXYGEN DOUBLE BOND (1) G. 0. Dudek and R. H . Holm, J . A m . Chcm. SOC.,88, 2089 Sir: (1981). a-Lumicolchicine, which is formed with 8(2) N. H. Cromwell, F. A. Miller, A. R. Johnson, R. L. Frank and D. J. Wallace, {bid., T i , 3387 (1949). lumicolchicine and y-lurnicolchicine in the irradia(10) American Chemical Society-Petroleum Research Fund Scholar, 1900.
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