866 COMMUNICATIONS

COMMUNICATIONS TO THE EDITOR

866 I

I "

I

'

.m

Vol. 84 b,

I ,ic

I

I

,m

I r

3.8

2.0

I

" "

I

-3 0

tn

6.2

Fig. 2.--N.m.r. spectrum of isodicyclopentadiene in CCla with tetramethylsilane as a n internal reference. The spectrum integrals are given above each major band. T h e insert is a ten-fold expansion of the olefin resonance.

Structures 111 and I V both appear consistent with the observed ultraviolet spectrum, Xmax (n-pentane) 268 mp (log 6 = 3.64) .I1 That the double bonds in isodicyclopentadiene are located as shown in I1 is indicated by the appearance of the n.m.r. spin-spin splitting pattern of the olefinic protons (Fig. 2 ) . The cracking reaction which leads to dihydropentalene must, therefore, proceed by initial isomerization of isodicyclopentadiene to V, which then undergoes a reverse Diels-Alder reaction (eq. 1). The facility of double bond isomerization in the cyclopentadiene series is expected on the basis of known precedents1* Acknowledgments.-\Ye are grateful to Larry Parker and Barbara Xlirth for assisting in the organic syntheses, and to the Xational Science Foundation (NSF G-15,561) and the Socony Mobil Oil Co. for financial support. (11) For cyclopentadiene in pi-heptane = 244 mp (log e = 3.40),12while for dimethylfulvene in isooctane XInSx = 265 ms (log = 3.9).la (12) R. W. Kieratead, I