methoxy phthalide isoquinoline (-)-cordrastine II2 (3c). In contrast, boron tribromide under similar reaction conditions was not selective and cleaved 3a to give mainly the corresponding tetraphenol.2 This may be related to the stronger nucleophilic character of the bromide ion.The above transformations demonstrate that boron trichloride can be used to selectively cleave a methylenedioxy group in methoxy-substituted aromatic compounds.Experimental Section® 4,5-Dimethylcatechol (lb).-To 378 mg (2.5 mmol) of 4,5methylenedioxy-o-xylene4 (la) dissolved in 70 ml of methylene chloride was added at room temperature 5 ml of a methylene chloride solution containing 585 mg (5 mmol) of boron trichloride. The solution was stored at ambient temperature for 3 hr; 5 ml of methanol was added and evaporated. The residue was crystallized from a mixture of benzene and petroleum ether to give 300 mg (80%) of lb, mp 89-91°, identical in mixture melting point and tic with authentic 4,5-dimethylcatechol.6 Under these reaction conditions 4,5-dimethoxy-o-xylene6 (lc) was recovered

The results of a complete analysis of the proton spectra of altersolanol B acetonide indicate that this compound exists preferentially in the half-chair conformation corresponding to that favored by the parent pigment in the solid state, as shown by previous X-ray studies. In contrast, the triacetate derivative apparently adopts the alternative half-chair conformation.Les rtsultats d'une analyse compltte r.m.n. de l'altersolanol B acttonide indique que ce compost existe prtftrentiellement sous la forme demi-chaise correspondant a celle favoriste par le pigment de base dans I'ttat solide, comme l'ont montr6 de prictdentes etudes rayons-X. En revanche, le dtrivt triacttate adopte apparemment la conformation demi-chaise alternative.Canadian Journal of Chemistry, 50, 122 (1972) In an earlier paper on some metabolites of Alternaria solani (I), structures were proposed for altersolanol B (1, R = R' = H), its triacetate (1, R = R' = Ac) and isopropylidene (2) derivatives. To confirm the assigned structures and to obtain information bearing on the probable conformations of these materials, a complete analysis of the proton spectrum of acetonide 2 was undertaken. In the interim Noda et al. (2) reported the results of their structural study of bostrycin (3), a closely related tetrahydroanthraquinone pigment. These authors found that treatment of hydrogenation products of 3 with p-bromobenzoyl chloride in pyridine yielded a crystalline ester which was subsequently hydrolyzed in these laboratories to give altersolanol B as judged by t.1.c. and U.V. spectra. X-Ray diffraction results for the p-bromobenzoate 1 (R = H, R' = p-BrC,H,CO) were presented by Takenaka et al. (3). As a further check on the correspondence between the two pigments a sample of acetonide 2 was treated with p-bromobenzoic anhydride in tetrahydrofuran containing some y-dimethylaminopyridine to yield an acetonide ester. Upon removal of the isopropylidene group, the resulting p-bromobenzoate was compared to an authentic sample of the degradation product obtained by Noda et al. mixture m.p., i.r. and U.V. spectra and specific rotation. Consequently, the structures originally proposed are undoubtedly correct but the question of preferred conformation remained.In addition to the methyl proton absorptions, the high field region of the proton spectrum of 2 consists of two overlapping AB patterns one of which is part of an ABX system; since the two AB patterns are long-range coupled a better description of the spin system may be ABMNX. To Can. J. Chem. Downloaded from www.nrcresearchpress.com by 34.214.212.150 on 05/11/18For personal use only.

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NotesH2 (1170 ml) had ceased. The catalyst was removed by filtration (Filter-Cel) and washed with fresh ethanol. The combined filtrates were cautiously neutralized with saturated NaHCOs and concentrated at reduced pressure to ca. 200 ml. This residue was diluted with benzene, washed with H20, and dried (Na2S04). Solvent removal gave a light yellow solid which was filtered through silica gel with 7:3 benzene-ether to give 15.4 g of light tan solid. Crystallization from CH2Cl2-ether gave 11.72 g (71.3%) of dione 2b as fine white needles, sintered at 171°, mp 173-175°. The analytical sample was prepared by a second crystallization from CH2Cl2-ether of similarly prepared material: mp 170.5-174°; uv max (C2H5OH) 222 nm (e 4750); ir (CHCls) 1740 (C-17 C=0), 1714 (C-5 C=0), and 1638 cm-1 (isoxazole);[a] 25d +122.0°(c 0.895, CHCls); mass spectrum (70 eV) m/e 329 (M+) and 110 (base peak); nmr (CDCls) 0.99 (s, 3, C-18 CHS), 2.20 (s, 3), and 2.37 ppm (s, 3, 2 isoxazole CH3); ORD (dioxane) [o+so +560°, [a]2$2 ±0°, [a]244 -938°( sh), [a]276 -2276°( min), [a)295 ±0°, and [ ] 7 +2926°(max).

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