4244
ize to @-lactoneIX. The isomerization of I to IV does not distinguish between paths A and B. Irradiation of x (R = C6H5; R ' = p-CH3C6H4)gives IX (R = C6Hj; R ' = p - C H & , H 4 ) . This result is consistent only with path B. The product shows: : :A 5.51 p ; U A = 6 5.29, V D = 6 5.84 (JAR= 7 cps), and is identified as IX rather than VI1 by the fragmentation of the parent ion (m/e 238) Of IX (R = C6Hj; R' = P - C H ~ C ~ Hto A) phenylketene radical cation (m/e 118, 40.6 % of base). The isomerization of I and I1 to IV has some generality. A variety of a-substituted cinnamic and crotonic acids (XIa-e) give @-lactones. @-Lactoneshave not yet hv
( 5 ) The cis and t r a m assignments are based on comparison of J A R in each case with J A Bfor the cis and trans isomers XIV and XV. (6) C. S. Wood and F. B. Mallory, J . Org. Chem., 29, 3373 (1964). (7) M. V. Sargent and C. J. Timrnons, J . Chem. Soc., 5544 (1964).
R" Xa, R
C6Hb; R ' = C6Ha; R" = H b , R = CH3; R ' = CeH;; R" = H C, R = CgH5; R ' = CH3; R" = H d , R = CeHj; R ' = C6Hj; R" = C8Hj e, R = C6Hs; R ' = CH3CBH4; R" = H =
0. L. Chapman, W. R. Adams Department of Chemistry, Iowa State Utzicersity
Ames, lon'a 50010
been isolated from cinnamic or crotonic acid. The photochemical synthesis of @-lactones has substantial advantages over other methods in ease and in producing the cis-lactone as the major product. Irradiation of the a,@-unsaturated amides XI1 and XI11 in degassed solution gives in each case the cisand trans-0-lactams in the yields indicated, together with other products. The trans-p-lactam XIV (mp 127-128"), which has been identified by comparison 0
jC6" + c&p: +
I Pyrex benzene 70 h r
XI1
c6H5
CGH~ 13%
2.5%
XVI (mp 154-155'j5 shows A ~ : ~5.67 ~ ' 1.1; ' U A = 6 4.87, v g = 6 5.12 (J.4,) = 6.0 cps). The trans isomer XVII (mp 124-125O)j shows 5.67 p ; U . ~= 6 4.15, ull = 6 4.62, J.&I~ = 3.0 cps. Both XVI and XVII give intense parent ions (m/e 223) and fragment ions at m/e 180. The photochemical production of the cis-@-lactamsin this series is of particular importance since these compounds are not easily available by other procedures. Irradiation of I1 or XI1 in the presence of iodine or oxygen gives the corresponding Acknowledgment. This research was supported by a grant from the National Science Foundation (GP 6740).
XVI
3% XVIT
Receiced M a y 20, 1967
Pyracylene. A Pentalenoid System?
Sir: Although Hiickle's 4n 2 rule strictly applies only to monocyclic systems, polycyclic unsaturated 411 2 systems also appear to possess the properties attributed t o aromatic hydrocarbons. T o account for the similarities in properties of the two types of unsaturated species Platt' proposed that the polycyclic system can be treated in terms of their 412 2 peripheries in which the cross-links only cause a small perturbation. We wish to consider the extension of such a model to molecules possessing 471 perimeters. In particular, we were interested in that subclass of these latter types that maintain a nonbonding energy level. HMO theory predicts that 4/1 monocyclic systems possess a degenerate pair of nonbinding levels occupied by two electrons, Application of the first-order perturbation treatment of Dewar and pet tit?^^ indicates that cross-linkage between alternate atoms only (Le., from starred t o starred or unstarred to unstarred in I and 11) removes this degeneracy but maintains one of the nonbonding levels. Cross-linkage to yield polycyclic sys-
+
+
+
xv -4-
C6H5??0
C&"
N\C6H5
other products
2.3% XN
with an authentic ample,^ shows ,,A, CHCI3 5.73 p ; V A = 6 4.25, VB = 6 4.94 (JAB = 3.0 cps). The cis isomer XV (mp 182-183') shows A~;pXC1'5.75 p, V A = 6 4.96, vu = 6 5.44 (JAB = 7.0 cps). Both cis and trans isomers give intense parent ions (m/e 299) and fragment ions at m/e 180 [(stilbene).+]. The cis-p-lactam (3) I
