REACTIONS OF ARYLAZIRINES
J . Org. Chem., Vol. 38, No. 7 , 1973 1333
spectively. Pmr spectra were recorded on JEOL MH-100 and C-60 HL spectrometers, and chemical shifts are reported with respect to internal TMS. Elemental analyses were performed by G. I. Robertson Laboratory, Florham Park, N . J. Preparation of 8a.-To a solution of 2.0 g (0.0093 mol) of T N T dissolved in a minimum amount of 1,3-dicarbomethoxyacetone at 25" was added about 3 ml of triethylamine. After standing a t room temperature for 10 hr, the reaction mixture was washed with anhydrous ether to remove the unreacted ketone. After several 100-ml washings the oily residue finally solidified to an orange powder, which when recrystallized from a 1:4 ether-ethanol mixture yielded cubic crystals of 8a: mp 116-117'; XmaX (MeOH) 446 nm; ir (KBr) 1730, 1662, 1610, 1555, 1490, 1450 cm-l; pmr ( n c c l s ) 6 1.36 [t, 9 H , +HN(CH&H3)3], 2.46 (s, 3 H , CHI), 3.18 [q, 6 H, + H N ( C H Z C H ~ )3.75 ~ ] , and 3.85 (each a singlet, 3 H each, COzCHa), 4.15 [d, 1 H , CHCOZCHI),4.42 (9, 1 H, CHNOZ),5.30 (d, 2 H, bridgehead protons), 11.08 [br, 2 H , HN(CHzCH3)3 and OH]. A pmr spectrum of the crude product showed the absence of 9a. Anal. Calcd for CZOH~UN~OII: C, 47.81; H , 6.02; N, 11.15. Fodnd: C, 48,04; H, 6.31; N, 11.09, Preparation of 8b and 10b.-To a solution of 2.0 g (0.0074 mol) of methyl 2,4,6-trinitrobenzoate dissolved in a minimum amount of 1,3-dicarbomethoxyacetoneat 50' was added 2 ml of tetrahydrofuran and 3 ml of triethylamine. After 4 hr at 25' the reaction mixture was washed with 75-m1 portions of snhydroufi ether. The resulting oil was dissolved in 35 ml of hot methanol and 90 ml of ether was added. After standing for 2 days a t 25", crystals were deposited on the bottom of the flask. Examination of these with a stereomicroscope showed two distinct crystalline forms. The crystals formed in larger quantity (ca. 80%) were a dull orange, while a smaller quantity of bright red-orange rrystals were also formed (ca. 20%). These crystals were separated manually under the microscope, and each was recrystallized from ether-methanol solution. The product formed in the largest amount was 8b, the remaining amodnt being lob. There was essentially no product left in the mother liquor. 8b had mp 142-143' and was hygroscopic; Xmax (MeOH) 499 nm; ir (KBr) 1742, 1725, 1665, 1610, 1555 cm-l; pmr (CDCla) 6 1.35 [t, 9 H , +HN(CHzCHa)a], 3.15 [q, 6 H , +HN(CHzCH,)s],
3.80 (s, 3 H , COzCHa), 3.85 (s, 6 H , two COzCHa), 3.82 (d, 1 H, CHCOZCHI),4.5 (q, 1 H , CHNOZ), 5.26 and 5.46 (two q, bridgehead protons), 12.1 [br, 2 H, +HN(CH&Ha)a and OH]. Anal. Calcd for C Z I H ~ U N ~ O C,I ~46.16; : H, 5.53; N, 10.25. Found: C, 45.68; €1,5.76; N, 9.99. 10b had mp 142-143'; hmar (MeOH) 497 nm; ir (KBr) 1755, 1740, 1650, 1610, 1555 cm-l; pmr (CDCl,) 6 1.35 [t, 9 H, +HN(CHzCHa)a],3.15 [q, 6 H , +HN(CHzCHa)al, 3.70 (s, 3 H , COzCHs), 3.8S (s, 6 H , two COzCHa), 4.80 (s, 1 H , CHCOzCHs), 5.2 (d, 1 H , CHNOZ),5.38 (br d , 1 H, bridgehead), 8.75 (s, 1 H, nitropropene nitronate), 12.1 [br, 2 H,+HN(CHZCHI)Iand OH], Anal. Calcd for CzlHt~NaOls: C, 46.16; H, 5.53; N, 10.25. Found: C, 46.96; H, 6.19;N, 9.42 Preparation of &.-A solution of 2 g (0.008 mol) of N-(2nitropheny1)picramide and 3 ml of triethylamine in the minimum amount of 1,3-dicarbornethoxyacetonenecessary for dissolution was allowed to stand at room temperqture for 4 hr. After washing the resulting reaction mixture with two 125-ml portions of ether an oily residue was obtained, which when recrystallized from a methanol-ether solution yielded orange crystals of 8c: mp 155'; Amax (CHIOH) 458 nm; ir (KBr) 1740, 1660, 1610, 1535 cm-l; pmr (CDC13) 6 1.10 [t, 9 H , + H N ( C H Z C H ~ )2.85 ~ ] , [q, 6 H, +HN(CH2CH3)3],3.70 and 3.78 (two s, 3 H each, two COzCH3), 4.1 (d, 1 H , CHCOZCH~), 4.3 (9, 1 H, CHNOZ),5.15 and 5.50 (two q, 2 H, bridgehead), 7.2-7.8 (m, 4 H, m-NOzCeH4), 12.4 [broads, 2 H, +HN(CHzCH3)3and OH]. Anal. Calcd for C Z ~ H I Z N ~ OC,I ~48.10; : H , 5.18; N, 13.48. Found: C, 47.93; H, 5.31; N, 13.34.
Registry No.-Sa, 38218-79-0; Sb, 38355-40-7; 8c, 38218-80-3; lob, 38413-80-8; TNT, 118-96-7; MTNB, 15012-38-1; NPP, 38229-29-7; 1,3-dicarbomethoxyacetone, 1830-54-2. Acknowledgments. -The authors wish to thank the Army Research Office at Durham, the Research Corporation, and the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this work.
Photochemical Transformations of Small Ring Heterocyclic Compounds. XLVIII. Further Studies on the Photocycloaddition and Photodimerization Reactions of Arylazirinesl ALBERTPADWA,*'
J O E L SMOLANOFF,3 AND
8. I. WETMORE, J F ~ . ~
Department of Chemistry, State li'niuersity of Xew York dt Buffalo, Buffalo, Kew York 1.!+214 Received November 29, 1972 Further evidence for the mechanism of the photodimerization of arylazirines was obtained by irradiating a mixture of phenyl- and diphenylazirine. The formation of a mixture of endo- and ezo-2,4,5-triphenyl-1,3diazabicyclo [3.1.0]hex-3-ene is rationalized in terms of I ,3-dipolar addition of the nitrile ylide derived from diphenylazirine onto the C-N double bond of phenylazirine. Irradiation of methyl- and dimethylphenylazirine in an inert solvent gave 1,3-diazabicyclo[3.1.0]hex-3-enesas primary photoproducts. The initial photodimers undergo subsequent photoreaction. The products formed depend on the substituent groups, the time of irradiation, and the particular solvent employed. The photocycloaddition of arylazirines has been found to proceed with a wide variety of dipolarophiles and provides a synthetic route into systems otherwise difficult to prepare.
I n earlier papers we have shown that arylazirines undergo photocycloaddition with electron-deficient olefins to give AI-pyrroline derivatives.ls5 The formation of the adducts was interpreted as proceeding by way of irreversible ring opening of the azirine ring (1) P a r t XLVII: A. Padwa, M. Dharan, J. Smolanoff, and 6 . I. Wetmore, Jr., J . Amer. Chem. Soc., 95, 1954 (1973). Part XLVI: zbzd., 95, 1945 (1973). (2) Alfred P. Sloan roundation Fellow, 1968-1972; National Institutes of Health Special Postdoctoral Fellow, 1972-1973. (3) NDEA Title I V Fellow, 1969-1971. (4) NSF Science Faculty Fellow, 1970-1971; Virginia Military Institute h d t y Fellow, 1971-1973. ( 5 ) A. Padwa and J. Smolanoff, J . Amer. Chem. SOC.,98, 548 (1971).
to form a nitrile ylide intermediate, which was subsequently trapped by a suitable dipolarophile. Arylazirines are also known to undergo photodimerization to 1,3-diazabicyclo [3,1.0]hex-3-ene~.~JThe formation of these dimers was rationalized in terms of 1,3dipolar addition of the initially generated nitrile ylide onto a ground-state azirine molecule. This conclusion was reached by a study of the variation of the quantum
a.
(6) A. Padwa. 8. Clough, Dharan, J. Smolanoff, and S. I. Wetmore, Jr., zbzd., 94, 1395 (1972). (7) N. Gakis, M. Marky, H. J. Hansen, and H. Schmid, Helu. Chim. Acta, 56, 748 (1972).
1334 J . Org. Chem., Vol. 58, No. 7 , 1973
PADWA, SMOLANOFF, AND WETMORE
yield for cycloadduct formation as a function of the concentration of added dipolarophile.6 According to this mechanistic scheme, it should be possible to generate a nitrile ylide from one arylazirine and intercept it with the C-N double bond of another azirine molecule. The present paper describes a reaction of this type which provides additional support for the mechanism of dimerization. To learn more about the effect of substituents in the azirine system, we also chose to study the photodimerization of methyl- and dimethylphenylazirine. An additional objective of this study was to examine the photobehavior of arylazirines with dipolarophiles other than electron-deficient olefins, and we herein report on such reactions. This process provides a synthetic route into systems otherwise difficult to prepare. Coirradiation of Phenyl- and Diphenylazirine. Further evidence for the mechanism of the photodimerization of nrylazirines was derived by irradiating an equimolar mixture of 2yhenyl- and 2,3-diphenylazirine (1 and 2). At 3130 A, the extinction coefficient for diphenylazirine is about 20 times that of phenylazirine, so that ca. 95% of the light is absorbed by diphenylazirine in the above experiment. Under these conditions a mixture of two 1:1 adducts was isolated. These were separated by liquid-liquid partition chromatography and identified as enclo- and exo-2,4,5-triphenyl-l,3-diazabicyclo [3.1.0]hex-3-ene (3 and 4) on the basis of the evidence presented below.
I
1
Ph
Ph Ph
5
H
3 or 4
1
PhCHO 3"
0
+
'LCHz
8"
Ph-C-NH,
PhPhr
I
A 0 Ph 6
azirine. On further irradiation (in cyclohexane), 3 and 4 are converted to triphenylpyrimidine ( 5 ) in low yield. When the irradiation of 3 (or 4) was carried
1
out in methanol, two new compounds were formed in addition to 5 (5%). These structures have been assigned as N-methoxy met hyl-2,4,5-triphenyl-2,3-dihydroimidazole (7) and N-methoxymethyl-2,4,5-triphenylimidazole (8). Treatment of 8 with aqueous acid afforded triphenylimidazole. The formation of 7 and 8 can be attributed to the addition of methanol to the azomethine ylide9,'O formed on irradiation of 3 (01'4).
2
"YN H
3
"J/" Ph 4
"X" H
Ph
3 or 4 H
The component of shortest retention time, 3 (20% of the 1 : l adducts), mp 176-177", had the following nmr spectrum (CDC13, 100 MHz) : aromatic protons at 7 2.70 (15 H, m) and singlets a t 8.26 (1 H ) , 77 Tetrabromodiazocyclopentadiene (3) had been previously prepared,s but its decomposition to the carbene had not been studied. We thought that it would be of interest to study what effect four large bromine atoms would have on the reactions of the carbene. Thus, wc now wish to report a new synthesis of 3 and a study of its photolytic decomposition in the presence of olefins. Synthesis of Tetrabromodiazocyclopentadiene (3).In 1963, a small amount of 3 was prepared in 15% yield from cyclopentadiene.8 We devised an alternate synthesis to avoid the preparation of large quantities of diazocyclopentadiene, which has reportedly undergone (7) M. Jones, Jr., and K. R. Rettig, J . d m e r . Chem. Soo., 87, 4013, 4015 (1965).
(8) D. J. Cram and R. D. Partos, ibid., 86, 1273 (1963),
