J. Org. Chem. 1987,52, 3457-3461 58.5 (d), 83.6 (s),224.4 ( 8 ) ; mass spectrum (70 eV), m / z (relative intensity) 202 (molecular ion, 12.6), 109 (8.9), 108 (loo), 107 ( 3 1 8 , 95 (22.0), 91 (12.2), 79 (16.5), 77 (19.6). Anal. Calcd for C13H1402:C, 77.20; H, 6.98. Found C, 77.47; H, 7.00. Method B. Compound 3a (500 mg, 1.44 mmol) and sodium chloride (300 mg, excess) were suspended in dimethyl sulfoxide (DMSO, 30 mL). The reaction mixture was heated at 150 "C for 1.5 h; slight darkening of the reaction mixture occurred, and a gas was evolved slowly during this period. The reaction mixture was then cooled to room temperature and water (150 mL) was added. The resulting mixture was extracted with methylene chloride (3 X 25 mL), and the combined organic layers were washed with water (3 X 30 mL), dried (anhydrous magnesium sulfate), and filtered. The filtrate was concentrated in vacuo to afford crude 4 as a white solid. Vacuum sublimation of this material [150 "C (0.05 mmHg)] afforded pure 4 (285 mg, 97%). Dimethyl 3,6-Dichloropentacyclo[6.5.0.0*~1z.06~'o.0g~'3]trideca-2,6-diene-2,7-dicarboxylate (6). A Suspension of 3a (1.0 g, 2.9 mmol) in phosphorus trichloride (6 mL) was cooled via application of an external ice bath. To this stirred suspension was added phosphorus pentachloride (3.00 g, 14.3 mmol) in small portions during 30 min. The reaction mixture was stirred for 1 h after all of the PC15had been added. The reaction mixture was then refluxed overnight. The resulting mixture was cooled to room temperature and poured over crushed ice (100 g). The resulting suspension wax extracted with methylene chloride (3 X 50 mL), and the combined organic layers were washed with water (3 X 50 mL), dried (anhydrous magnesium sulfate), and filtered. The filtrate was concentrated in vacuo to afford crude diacid 5 as a light brown microcrystalline solid. This material was dissolved in methanol (10 mL) that contained concentrated sulfuric acid (2 drops), and the resulting solution was refluxed overnight. The reaction mixture was cooled and diluted with water (60 mL), and the resulting mixture was extracted with methylene chloride (3 X 30 mL). The combined organic layers were washed with water (4 x 50 mL), dried (anhydrous magnesium sulfate), and filtered, and the filtrate was concentrated in vacuo. Crude 6 was thereby obtained as a light brown microcrystalline solid. This material was recrystallized from ether to afford pure 6 as colorless prisms (369 mg, 36%): mp 138-139 "C; IR (KBr) 2949 (s), 2890 (s), 2849 (m), 1722 (s), 1698 (s), 1626 (s), 1610 (m), 1440 (s), 1255 cm-' (9); 'H NMR (CDCl,) 6 1.51 (AB, J A B = 10.5 Hz, 1H), 1.60 AB, JAB = 10.5 Hz, 1 H), 2.42 (m, 2 H), 2.80 (m, 2 H), 3.15 (m, 2 H), 3.70 (s,6 H), 3.78 (m, 2 H); 13CNMR (CDC1,) 6 35.2 (d), 37.0 (t), 39.7 (d), 40.5 (d), 51.9 (d), 53.2 (q),126.9 (s), 141.5 (s), 165.8 (9); mass spectrum (70 eV), m / z (relative intensity) [no molecular ion] 184.0 (100.0), 124.9 (93.4). Anal. Calcd for Cl7Hl6Cl2O4:C, 57.48; H, 4.54. Found: C, 57.39; H, 4.37. Attempted Intramolecular [2 + 21 Photocyclization of 6. A solution of 6 (200 mg) in degassed ethyl acetate (250 mL) was irradiated with a 450-W Hanovia medium-pressure mercury lamp (Pyrex filter) for 24 h. Removal of solvent in vacuo afforded only unchanged starting material (194 mg). No reaction occurred even when considerably longer irradiation times were employed (i.e., 48 and 72 h, respectively).
Acknowledgment. Financial support of this study by the Air Force Office of Scientific Research (Grant AFO SR-84-0085),The Robert A. Welch Foundation (Grant B-963), a n d t h e N o r t h Texas S t a t e University Faculty Research Committee is gratefully acknowledged. T h e X-ray crystallographic structure determination of 3a was supported i n p a r t b y t h e Office of Naval Research Mechanics Division.
Registry No. 1, 2958-72-7; 3a, 108744-07-6;4, 108744-08-7; 5, 108744-09-8;6, 108744-10-1;ethyl diazoacetate, 623-73-4.
Supplementary Material Available: A list of atomic coordinates and equivalent isotropic displacement parameters, bond lengths, bond angles, anisotropic displacement parameters, and H-atom coordinates and isotropic displacement parameters for 3a (5 pages). Ordering information is given on any current masthead page. 0022-3263/87/1952-3457$01.50/0
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Intramolecular [2 21 Cycloadditions of Ketenes to Carbonyl Groups. A Novel Synthesis of Substituted Benzofurans William T. Brady,* Yun-seng F. Giang, Alan P. Marchand,* and An-hsiang Wu
Department of Chemistry, North Texas State University, Denton, Texas 76203-5068 Received February 11, 1987 T h e r e is considerable current interest in synthetic applications of intramolecular [2 21 cycloaddition reactions of ketenes with carbon-carbon double bonds1 and with ketone and aldehyde carbonyl groups.2 We recently reported t h a t (o-carbony1phenoxy)acetylchlorides can be readily dehydrochlorinated t o afford t h e corresponding ketenes, which then undergo facile intramolecular [2 + 21 cycloadditions t o form t h e corresponding tricyclic @-lactones. Decarboxylation of these lactones t h e n occurs spontaneously, thereby affording the corresponding benzofuran in 53-82% yield (Scheme I).2 I n order to further delineate t h e scope and limitations of this novel synthesis of substituted benzofurans, we have explored new methods to generate ketene intermediates for use in intramolecular cycloaddition reactions. We now report t h e results of our study. T h e method utilized for t h e synthesis of t h e (ocarbony1phenoxy)acetic acids that were employed as substrates in this study is illustrated in Scheme I1 for t h e preparation of [(o-formylphenoxy)phenyl]aceticacid. Williamson ether syntheses were carried out via reaction of appropriately substituted phenoxide anions with substituted a-bromoacetic acids (see Experimental Section). On occasions when oily (0-acy1phenoxy)acetic acids were prepared that could n o t be recrystallized, i t proved expedient t o purify t h e m via the corresponding dicyclohexylammonium salt.3 These salts, prepared conveniently b y reaction of each of t h e crude acids with dicyclohexylamine, could b e purified simply b y washing with ligroin. T h e salts thereby obtained proved to be suitable for direct utilization in the one-pot ketene cycloaddition procedure (method B) without t h e necessity of prior conversion to t h e free acid. Three different methods were t h e n utilized to generate t h e corresponding ketenes from these (ocarbony1phenoxy)acetic acids, as follows. Method A. Base-promoted elimination of hydrogen chloride from acid chlorides of t h e type R,CHC(O)Cl is one of t h e classical methods by which ketenes have been generated t r a d i t i ~ n a l l y . ~T h u s , t h e (o-carbonylphen0xy)acetic acids were converted into t h e corresponding acid chlorides via reaction with 5-8 equiv of oxalyl chloride in benzene at ambient temperature for 4-8 h. Excess oxalyl chloride was removed in vacuo, and the crude acid chloride was then added very slowly t o a refluxing solution of triethylamine (3 equiv) in benzene. T h e fact that dehydro-
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(1) (a) Snider, B. B.; Hui, R. A. H. F.; Kulkarni, Y. S. J. Am. Chem. SOC. 1985,107, 2194. (b) Marko, I.; Rosmans, B.; Hesbain-Frisque, A.; Dumas, S.; Ghosez, L.; Ernst, B.; Greuter, H. J. Am. Chem. SOC.1985, 107,2192. (c) Snider, B. B.; Hui, R.A. H. F.J.Org. Chem. 1985,50,5167. (d) Brady, W. T.; Giang, Y. F. J. Org. Chem. 1985,50,5177. (e) Kulkami, Y. S.; Snider, B. B. J.Org. Chem. 1985,50,2809. (0 Corey, E. J.; Desol,
M. C. Tetrahedron Lett. 1985,26,3535. (9) Kulkarni, Y. S.; Burbaum, B. W.; Snider, B. B. Tetrahedron Lett. 1985,26, 5619. (h) Ghosez, L.; Marko, I.; Hesbain-Frisque, A. M. Tetrahedron Lett. 1986, 27, 5211. (2) Brady, W. T.; Giang, Y. F. J. Org. Chem. 1986,51, 2145. (3) Klieger, E.; Schroder, E.; Gibian, H. Liebigs Ann. Chem. 1961,640, 157.
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