THE JOURNAL OF
Organic Chemistry 0Copyright 1979 by the American Chernii.a/ Sociciy
VOLUME 44, NUMBER 1
JANUARY 5,1979
Cycloadducts of Nitrosobenzene with Cyclic Dienones and Dienols Harold Hart,* Sambharamadom K. Ramaswami, and Rodney Willer Department of Chemistry, Michigan State linicersity, East Lansing, Michigan 48824 Received J u l y 24, 1978
Nitrosobenzene adds regiospecifically to cyclohexadienones 3 and 4, the oxygen of the nitroso group being oriented toward the carbonyl group in the adduct. Addition to eucarvone, a cycloheptadienone, was slower but also regiospecific in the same sense. The hexamethylcyclohexadienone 5 , however, gave both regioisomers in approximately equal amounts. Cyclohexadienols 13 and 14 add nitrosobenzene regiospecifically in two senses; the oxygen of the nitroso group is oriented toward the alcohol substituent,and the hydroxyl group is syn to the N-0 bridge. The N-0 orientation in addition to dienones and dienols is in accord with expectation from qualitative frontier orbital considerations, and the hydroxyl orientation in the dienol adducts may reflect hydrogen bonding in the transition state. 0
Various C-nitroso compounds readily form cycloadducts with conjugated T h e products are 3,6-dihydro1,2-oxazines I, potentially useful synthetic intermediates with
1
2 3 R 2 = R 3 = R4 = R 5 = H 3, R, = R , = H ; R , = R, = CH, 4 , R , = H; R, = R , = R, = C H ,
5, R:
=
R,
=
R,
functionality a t four contiguous carbon atoms since the C=C bond can be functionalized and the N-0 bond can be reductively cleaved. These possibilities have been used, for example, in amino sugar synthesis." T o extend the scope and synthetic utility of these reactions, we studied cyclic dienones and dienols as possible diene components in cycloadditions with nitroso compounds. We report here t h a t such cycloadditions to nitrosobenzene proceed readily, often with high yield and high regioselectivity.
=
R, = CH,
6 7 (51%) 8 (100%) 9 (and regioisomer 10; 100%)
Results
1:l mixture of 9 and its regioisomer 10 ( N bonded to C2 and
Cyclohexadienones 2-5 were allowed to react a t room temperature with nitrosobenzene in methylene chloride or carbon tetrachloride under a nitrogen atmosphere. Reactions were monitored by NMR and/or by disappearance of the green color of nitrosobenzene. T h e unsubstituted dienone 24 gave NMR evidence of reaction, but new peaks possibly due to the adduct 6 quickly reached a maximum area when the solution still appeared to contain 75% starting material, and attempts to isolate an adduct were unsuccessful. Methyl substitution on the dienones enhanced their reactivity toward cycloaddition. Thus, the tetramethyldienone 35 gave the crystalline adduct 7 ( m p 62-63 "C) in 51% yield, and the pentamethyldienone 46 gave a quantitative yield of 8 (mp 99-102 "C). Only a single regioisomer was obtained in each case, assigned structures 7 and 8 based on spectral and chemical evidence (vide infra). T h e fully methyl-substituted dienone 57 also added nitrosobenzene quantitatively, b u t an approximately
0 to Cg) was formed; only one isomer was isolated in pure form. Of all the dienones and dienols we report on here, only
0022-3263/79/1944-0001$01 .OO/O
the reaction of 5 gave both regioisomers. T h e only seven-membered ring dienone studied was eucarvone (11): which reacted quantitatively to give adduct 12 (mp 56-57 "C).
11
IH
(',
12 ( looy.~)
Cyclohexadienols reacted much more rapidly than the corresponding ketones. Thus, yields of 15 and 16 from 13 and
0 1979 American Chemical Society
1
2 J . Org. Chem., Vol. 44, No. 1, 1979
Hart, Ramaswami, and Willer
I
1.
13, R , = R, = R, = R , = H 14,R, = R 5 = H ; R , = R, = CH,
CH
t
-H*O
0
U
bond were the other way around in 16,18 could not have been formed by this reaction sequence. Finally, the 0 - H stereochemistry in 16 is assigned on spectral grounds. T h e IR spectrum showed a strong intramolecular hydrogen bond OH stretch at 3576 cm-’, unaffected by dilution. Also, comparison of 16 with a series of analogous alcohols (vide infra) shows that the chemical shift of the hydroxyl proton occurs a t much lower field (6 2.4 f 0.4) when the hydroxyl is “over” the N-0 bond than when it is “over” the C=C bond (6 1.2 f 0.1). A similar effect, though not quite as large, is seen with the C-H bond of the CHOH groups (6 3.4 f 0.1 when “over” the N-0 bond, 6 3.0 f 0.1 when “over” the C=C bond). These differences can reasonably be attributed to shielding by the C=C bridge and deshielding by the N-0 bridge. Structure of Adduct 8. The structure of 8 is based upon comparison of its NMR spectrum with that of 7, upon deuterium labeling, and upon comparison of the NMR spectrum of its reduction product 19 with that of 16. The bridgehead t
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