J . Org. Chem. 1989,54, 1342-1346
1342
with chloroform (2 mL). Organic phases were combined and evaporated, and the residue was subjected to crystallization or purification on a silica gel column. Alternatively, the protected phospholipids can be purified on silica gel columns and then subjected to a deprotection step. General Procedure for Synthesis of Phospholipid Analogues 5 and 6. To a crude reaction mixture containing the H-phosphonate 3 was added sulfur (2 equiv) in pyridine/toluene (l:l, v/v, 1 mL) or selenium (2 equiv) in dioxan (1mL), and the suspension was stirred for 2 and 10 h, respectively. The reaction mixtures were diluted with chloroform (30 mL) and washed with water or with 0.1 TEAB. Further workup and deprotection were the same as described for 4 with the exception that the deprotection was carried out in the presence of 1,2-ethanedithiol (10 equiv). 1,2-Dipalmitoyl-sn-glycero-3-H-phosphono-N-(tert -butoxycarbony1)ethanolamine (3b). Column chromatography: silica gel; eluent, toluene/ethyl acetate (l:l,v/v). Yield 98%. [.ImD +2.3' (c 2.6, CH2CLz). Rf0.60 (system F). For the 13Cand 31PNMR data, see Table I. 12-Dipalmitoyl-sn-glycero-3-phosphocholine(4a). Column chromatography: silica gel; eluent, CHC13/MeOH/H20 (6633:4, v/v). Yield 80%. [ a l m D +7.7' (c 2.0, CHC13/MeOH, 1:l). Rf0.45 (system B). For the 13C and 31PNMR data, see Table I. 12-Dipalmitoyl-sn -glycero-3-phosphoethanolamine(4b). Column chromatography: silica gel; eluent, CHC13/MeOH/Hz0 (100:15:1, v/v) and then CHC13/MeOH/H20(95352, v/v). Yield 86%. [ctI2OD +12.3' ( c 2.2, CHC13/MeOH, 91). Rf0.50 (system A). For the I3C and 31PNMR data, see Table I.
1,2-Dipalmitoyl-sn-glycero-3-phospho-~-serine (4c). Column chromatography: silica gel; eluent, CHC13/MeOH/H20 (65:25:4, v/v). Yield 81%. [aI2OD +12.5' (c 1.5, CHC13/ MeOH/H,O, 65:25:4, v/v). R, 0.40 (system B). For the 13C and 31PNMR data, see Table I. l,2-Dipalmitoyl-sn-glycero-3-thiophosphoethanolamine (5b). Column chromatography: silica gel; eluent, CHC13/MeOH (51,v/v). Yield 93%. [aIzoD +17.5' ( c 1.3, CHC13/MeOH, 1:1, v/v). R, 0.49 (system D). For the 13C and 31PNMR data, see Table I. 1,2-Dipalmitoyl-sn -glycero-3-thiophosphocholine(5c). Column chromatography: silica gel; eluent CHC13/MeOH (1:1, v/v). Yield 86%. +16.0° (c 2.0, CHC13). Rf0.60 (system C). For the 13C and 31PNMR data, see Table I. 1,2-Dipalmitoyl-sn -glycero-3-selenophospho-N( tert -butylcarbony1)ethanolamine (6a). Column chromatography: silica gel; eluent, CHC13/MeOH (6:1, v/v). Yield 98%. R, 0.55 (system E). For the 13C and 31PNMR data, see Table I. 12-Dipalmitoyl-sn -glycero-3-selenophosphoet hanolamine (6b). Column chromatography: silica gel; eluent, CHC13/MeOH (6:1, v/v). Yield 56%. [ctI2'D +17.6' (c 1.6, CHC13/MeOH, 2:1, v/v). Rf0.37 (system E). For the 13Cand 31PNMR data, see Table I. Anal. Calcd C37H7407PNSe:C, 58.8; H, 9.9; N, 1.9. Found: C, 58.5; H, 9.9; N, 1.7.
Acknowledgment. We are indebted to Prof. P. J. Garegg for his interest and to the Swedish National Board for Technical Development and the Swedish Natural Science Research Council for financial support.
Steady-State and Laser Flash Photolysis Studies of Norbornenobenzoquinones and Their Diels-Alder Adducts' G. Mehta,*VzaS. Padma,2aand S. R. Karra2" School of Chemistry, University of Hyderabad, Hyderabad 500134, India
K. R. Gopidas,2bicD. R. Cyr,zc,dP. K. Das,*yzc,eand M. V. George*s2b,c Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India, and Radiation Laboratory and Department of Chemistry, University of Notre Dame, Notre Dame, Indiana 46556 Received July 28, 1988
Results of a photochemical study based on nanosecond laser flash photolysis and steady-state photolysis are reported for several norbornenobenzoquinones and their rigid Diels-Alder adducts. Products isolated from steady-state photolysis of a few representative cases suggest that the preferred mode is intramolecular [2 + 21 cycloaddition wherever feasible, and triplets have been implicated in this photoreaction. The 337.1-nm laser pulse excitation of the substrates in benzene gave rise to triplets (XmmT = 390-580 nm), characterized by short lifetimes (21 ns-1.05 ps) in fluid solutions a t room temperature. The triplets were efficiently quenched by oxygen, ferrocene, p-methoxyphenol, HTEMPO, and azulene, but they exhibited reluctant quenching behavior toward DMHD and triethylamine. The lower limits of triplet yields ( @ ~ , l i for ~ ) most of the substrates were measured by energy transfer to 9,lO-diphenylanthracene (DPA). In some cases, the efficiency of energy transfer to DPA in benzene appeared to be small, probably owing to reversible charge transfer interaction competing favorably with energy transfer.
Introduction T h e interesting tricyclic quinone 2 (2,3-norbornenobenzoquinone) ,3a,b readily available from the endo adduct 1 of 1,3-cyclopentadiene and p-benzoquinone, has not re(1) Document No. NDRL-3114 from the Notre Dame Radiation Laboratory. (2) (a) University of Hyderabad. (b) Indian Institute of Technology, Kanpur. ( c ) University of Notre Dame. (d) Undergraduate research student from the University of Waterloo, Ontario, Canada. (e) Current address: 347A, Petroleum Laboratory, Research and Development, Philips Petroleum Company, Bartlesville, OK 74004. (3) (a) Diels, 0.;Alder, K. Ber. 1929,62, 2337-2372. (b) Meinwald, J.; Wiley, G. A. J.Am. Chem. SOC.1958,80,3667-3671. (c) Cookson, R. C.; Hill, R. R.; Hudec, J. J. Chem. SOC.1964, 3043-3062. (d) Cookson, R. C.; Hill, R. R. J. C h e n . SOC.1963, 2023-2026. (e) Cookson, R. C.; Grundwell, E.; Hill, R. R.; Hudec, J. J. Chem. SOC.1964, 3062-3075.
0022-3263/89/ 1954-1342$01.50/0
ceived much attention except for a few studies by Cookson and c o - w o r k e r ~ .Recently, ~~~ some of us4 have demonstrated the synthetic potential of 2 through Diels-Alder chemistry to prepare novel, strained polycyclic systems. In continuation, we became interested in utilizing the photochemistry of 2 and related quinones to gain access to highly strained quadricyclane derivatives 3. In general,
@=@&,.&) 0
0
-1
2
0
3
(4) Mehta, G.; Padma, S. J. Am. Chem. SOC.1987, 109, 7230-7232.
0 1989 American Chemical Society
J. Org. Chem., Vol. 54, No. 6, 1989 1343
Flash Photolysis Studies of Norbornenobenzoquinones
Scheme I1
Chart I CI. ,CI
2,R-H
4, R = Br
-4
hexane
11,R.H 12, R
=
OCH,
BI
Scheme I 21
17
whereas the dibromo derivative 4 was prepared as per the pathway shown in Scheme I. All these compounds were fully characterized on the basis of their 'H NMR and 13C NMR spectra (vide Experimental Section). Diels-Alder reaction between 1,3-cyclopentadiene and the quinones 2 and 4 gave a mixture of endo,anti and endo,syn adducts 9 and 11 (35:65)3c and 10 and 12 (38:62), respectively. These adducts were separated by chromatography and characterized spectroscopically. Structures 9 and 11 were further confirmed through their intramolecular [2 21 photocycloaddition to the corresponding heptacyclic caged compounds 19 and 20, respectively (Scheme 11). Addition of 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene to 2 furnished the endo,anti and endo,syn adducts 13 and 14, respectively, in the ratio of 77:23. Irradiation of the major component 13 led to the formation of the [2 21 photocycloadduct 21 (Scheme 11). The syn-bisnorbornenoquinone 7 was prepared from the endo,syn adduct 12 of the dibromoquinone 4 and cyclopentadiene, as shown in Scheme I. The orange-yellowish 7 exhibited a five-line 13C NMR spectrum, with diagnostic signals a t 6 48.1, 73.9, 145.7, 160.3,'and 181.1. The antibisnorbornenoquinone 8 was prepared from the endo,anti adduct 9 of quinone 2 and c y ~ l o p e n t a d i e n eas , ~ ~shown in Scheme 11. The glistening orange quinone 8 also exhibited a five-line I3C NMR spectrum with signals a t 6 48.1, 74.0, 142.7, 160.3, and 181.1. T h e two quinones 7 and 8 had nearly identical IR, l H NMR, and 13C NMR spectra. 2. Laser Flash Photolysis Studies. Upon 337.1-nm laser flash photolysis, benzene solutions of substrates 2, 4-14 produce absorbance changes due to the formation of phototransients that are best characterized as triplets. Representative transient spectra and kinetic traces are shown in Figure 1. The transients decay by clean firstorder kinetics over microseconds. In most cases, the decay lifetimes were measured as a function of the ground-state concentration of the substrates, and the intrinsic lifetimes were obtained by extrapolation to the zero concentration. T h e kinetics and spectral data are summarized in Table I. The triplet assignment of the observed transients was based on their quenching behavior toward various reagents (see Table I), well-recognized for their efficient interaction
+
P
the photochemistry of norbornadiene derivatives leading to quadricyclanes has been of current interest from the viewpoint of solar energy tora age.^ As reported earlier3c and also observed in the present study, the irradiation of 2 under a variety of conditions gave only intractable, polymeric materials. Recently, however, a report by Suzuki e t a1.6 has appeared on isomerization of certain norbornenonaphthoquinones and norbornenobenzoquinones to the corresponding quadricyclanes. Because of the photochemical significance, we became interested in a nanosecond laser flash photolysis study of 2, related quinones and their Diels-Alder adducts (Chart I). T h e results of this time-resolved study combined with the preparative photochemistry in representative cases are presented in this paper.
Results and Discussion 1. Preparative Chemistry. The norbornenoquinones 2, 5, and 6 were prepared as per reported procedure^,^^-^ (5) (a) Jones, G. II; Ramachandran, B. R. J. Org. Chem. 1976, 41, 798-801. (b) Heutala, R. R.; Little, J.; Sweet, E. Solar Energy 1977,19, 503-508. (c) Scharf, H.-D.; Fleischhauer, J.; Leismann, H.; Ressler, I.; Schleker, W.; Weitz, R. Angew. Chem., Int. Ed. Engl. 1979,18, 652-662. (d) Maruyama, K.; Terada, K.; Yamamoto, Y. J. Org. Chem. 1981, 46, 5294-5300. (e) Barsub, N.; Chang, S.-C.; Kutal, C. Inorg. Chem. 1982, 21, 538-543. (0 Fife, D. J.; Moore, W. M.; Morse, K. W. J. Am. Chem. SOC.1985, 107, 7077-7083. (6) Suzuki, T.; Yamashita, Y.; Mukai, T.; Miyashi, T. Tetrahedron Lett. 1988, 29, 1405-1408.
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J . Org. Chem., Vol. 54, No. 6, 1989
Mehta et al.
Table I. Spectral and Kinetics Data of the Triplets of Norbornenobenzoquinone and Related Systems in Benzene at 298 K h,~,b 109 ~
- s-l 1
substrate
XmaxTIB nm
TT,~ ps
IT,,^^
0,
HTEMPO'
ferrocene
azulene
PMP'
2
510 530 580 470 550 550 420 420 390 420 410 400
0.79 0.054d 0.24d 1.6 0.76d 0.67d 0.25
0.7 e e 1.0 e e 0.8 e 0.9 0.6 0.9 1.0
1.8 0.85 1.5 1.3 3.0 1.7
3.4 5.2 5.9 8.2 4.8 3.0 0.59
11.0 12.0 14.0 14.0 12.0 7.4 3.4 6.7 3.5 7.4 5.3 5.3
3.9 18.0 12.0 11.0
7.9 11.0 10.0 11.0 11.0 7.5 2.4
4
5
6 7 8 9 10 11 12 13 14
0.021d 0.39 0.080 0.55 0.54
2.6
2.8 2.9 1.7 1.3 1.9
f
0.97 1.4 1.2 1.2
f f
1.5
f f f 2.8
f
f
1.9 3.6 1.8 2.6
DMHDc 0.45
f
7.4 4.8
