5800 acetonitrile, acetic anhydride, etc., are treated here as one two-carbon reagent with f list 30, yielding an attached two-carbon unit (acetyl) of f list 20 in the product of a 31 half-reaction (acylation, Tables IV and Vi). (21) R. E. Ireland “Organic Synthesis”, Prentice-Hail. Englewood blffs. N.J.. 1969. (22) (a) E. J. Corey, W. T. Wipke, R. D. Cramer, and W. J. Howe. J. Am. Chem. Soc., 94, 421 (1972), and adjacent papers; (b) E. J. Corey, 0. Rev. Chem. Soc., 25, 455 (1971). (23) “Computer Representation and Manipulation of Chemical Information”, W. T. Wipke, S.R, Heiler. R. J. Feldman. and E. Hyde, Ed., Wlley. New York, N.Y., 1974. (24) There are a few cases in Table V-IX in -which the half-span is different in substrate and product, essentially in 12 and one variant each of A3 and B3. The labeled half-span is always the greater. The f llsts for A, and B1 are sometimes listed with fa = 0 since any function of 0is either disallowed or changes the label. See Appendix for discussion. (25) The eight possible f lists for half-reactions yield = 36 possible combinations of full f lists of six digits for the full slx-carbon product strand. Excluding f ’ = 101, there are only (): = 26 combinatlons. In Table XII, the rarely accessible f ’ = 000.000 (cf. Wurtz reaction) is omitted. (26) A few oxidative and redhtive couplings with reasonable precedent, as A2aA2 or C2C2 (Table IV), have been added to the list of constructions, to make 196 full produGts and 367 reactions. (27) N. Anand, J. S. Bindra, and S. Ranganathan, “Art in Organic Synthesis”, Holden-Day, Sen Francisco, Calif., 1970, provkles a convenient summary collection for examining how many syntheses have utilized this principle of functionality dissection; the Torgov and related steroid syntheses are found on pp 96, 170, 177. (28) The iattmost construction is found in Table Xlll only by assumlng the double bond to be extraneous off-strand and looking up 000.2 Insteadof ooo.2n. (29) The Sequence includes a Robinson annelation (steps 1 and 2). Another option for step 2, construction of bond 5-6 for the other A2-13 (Michael addition), is precluded by the maximum u list in Table Xi which disallows u = 4 at the 0atom of 13 (atom 4). (30) Cyclization constructions may be further circumscribed by restricting the half-reactions that are viable_for given ring sizes; in the particular case in Figure 3, reactions A? or 22 would presumably be disallowed.
’
’
(31) An example of half-reaction 5 Is the alkylation of unsaturated sulfones:
R-X
PkSO,-CH-CH=CH,
--+
R
I
Ph--SO,-CH-CH=CH1
(A)
(i)
if there were no hyerogen on a,the first tautomer (A) must be the product (ua = 3) but. if (as shown) urn= 2 in the product, then the product structure is expected to be the conjugated (E). Propertv the lower substrate should be labeled C3, but both are subsumed under the E3 label because they are so clearty one reactlon family and both yleld the same products. (32) Reactlons 11 and 12 are further restricted in the tables to u, S 2 in the substrate, forbidding displacements at tertiary carbons as characteristic of SN2 reactlons. The few such constructions which occur at tertiary carbons are usually olefinic cyclizations to tertiary leaving groups. The catalog can be adapted in use to include these but their exclusion here is justlfled by their rarity: if tertiary 1, and 12 a carbons were allowed. too many nonviable constructions would turn up in the general sets of routes derived from them in any systematlc search protocol. (33) Presented at the Synthesis Design Symposium, Louvaln, Belgium, March 1974 Top. Cum.Chem., in press.
Atomic Oxygen. IV. Rearrangements in the Reactions of Oxygen (3P) Atoms with Cyclic and Bicyclic Hydrocarbons James J. Havel* and Kam H. Chan Contributionfrom the Department of Chemistry, Rice University, Houston, Texas 77001. Received February 24, 1975
Abstract: The gas phase reactions of ground state (3P)oxygen atoms with several cyclic and bicyclic hydrocarbons have been examined. The atomic oxygen was produced by the mercury photosensitized decomposition of nitrous oxide. The organic substrates studied were: cyclohexene, norbornene, 1,4-~yclohexadiene,norbornadiene, cyclobutene, and bicyclo[ 1.1.O] butane. Extensive rearrangements occur during these reactions. Spectra of a novel compound, endo-bicyclo[2.1.1]hexane-5-carboxaldehyde, are reported.
The reactions of atomic oxygen are of demonstrated importance in the chemistry of the upper atmosphere* and of c o m b ~ s t i o n .Synthetic ~ applications of oxygen atom reactions are also being explored.’ Cvetanovic has made a number of interesting mechanistic observations about these atomic proce~ses.~ Ground state (3P) oxygen atoms are conveniently procljired in the gas phase by the mercury photosensitized decomposition of nitrous oxide (eq l and 2).4,5
-
Hg(’So) Hd3P,)
+ N,O
+ hy
-+
Hg(’So)
Hd3P1)
+
N,(’Z)
Scheme I
$c=c&’ + OCP)
+ O@)
I
J 0’
0
I . RF-Cb’
(1) (2)
While O(3P) reacts sluggishly with most alkanes, the reaction with alkenes is quite efficient. The reaction of atomic oxygen with acyclic olefins produces approximately equal quantities of epoxides and carbonyl compounds. The latter Journal of the American Chemical Society
products are of particular interest, because their formation must involve rearrangement of a substituent of the olefin. Cvetanovic has proposed4 that O(3P) atoms add to olefins to form short-lived 1,3 biradicals (Scheme I). These
”-J
$C-C$’
I
J
I
YO
0
II
RC-~’R
/ 97:20 / October 1 , I975
$C-C$’
R’$C-CR’
II
5801 biradicals can either close to epoxides or rearrange to aldehydes and ketones. The l ,2 migration of a hydrogen atom is intramolecular, but alkyl groups become at least partially detached during rearrangement. The migrating alkyl radicals can be scavenged by molecular oxygen. The rearrangement of hydrogen atoms and alkyl radicals in 1.3 biradicals is significant, because these groups do not commonly migrate in monoradical systems. The reactions of O(3P) with molecules which contain more complex patterns of unsaturation than acyclic olefins have shown some unusual rearrangements or fragmentations. Product studies on the reactions of allenes? cyclopropenes,' cyclopentene,* and 1,3-butadiene' have been published. We report here the products of the reactions of atomic oxygen with cyclohexene, norbornene, 1,4-cyclohexadiene, norbornadiene, cyclobutene, and bicyclo[ 1.1.O]butane.
ring closure at either carbon (cyclobutanecarboxaldehyde) or oxygen (dihydropyran), and by hydrogen abstraction (2and 4-pentenals). An extension of this mechanism to the reaction between cyclohexene and atomic oxygen is shown in Scheme 11. 1,2Scheme I1
2
4
t
Results and Discussion A. Reaction Conditions. The apparatus for the production and reaction of oxygen (3P) atoms has been described previously.6 The atoms are made by gas phase photolysis of a mixture of nitrous oxide, the hydrocarbon substrate, and mercury vapor. The total pressure before photolysis was about 0.9 atm, and the reaction temperature was 25-29O. Product yields reported below are based on the quantity of nitrogen produced (eq 2). While total product yields from atomic oxygen reactions are usually quite good, substrates which polymerize rapidly, i.e., norbornadiene, exhibit limited conversions of substrate to oxygenated product. In these cases, the photolysis is self-terminated when the lamp becomes coated with a thin film of uv-opaque material. Two experimental conditions are used to limit the reactions to primary processes. First, a high ratio of nitrous oxide to substrate (>15) is maintained in order to minimize mercury photosensitized reactions of substrate or products. Second, conversion of organic substrate was limited to
