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Synthesis of 3 from 11. A solution of 11 (250 mg, 1.45 mmol) in 80% aqueous AcOH (25 mL) was refluxed for 0.5 h. The solvent was evaporated in vacuo to afford a yellow solid. Pure product (3) was obtained in 82% yield by recrystallization of the crude yellow solid (EhO/pentane, 1:4), mp 124-127 "C (lit.3 mp 124-125 "C).Synthesis of 1,2:3,4-Bis-0 -( l-methylethylidene)-5bromo-5-deoxyxylitol. Into a solution of 1,2:3,4-bis-0-(1-methylethy1idene)-5-tosylxylito18 (38.5 g, 0.1 mol) in 250 mL of DMF was added lithium bromide (21.0 g, 0.2 mol). After the solution was stirred at 90 "C for 2 h, it was cooled to room temperature, poured into icewater, and extracted with ether. The extract was washed with brine, dried over MgS04, and filtered, and the filtrate was evaporated. The residue was distilled under reduced pressure to give 1,2:3,4-bis-O-(l-methylethylidene)-5bromo-5-deoxyxylito1(26.0 g, 0.088 mol) in 88% yield bp 97.5-102 "C (2-3 mm); IR (neat) cm-'; 'H NMR (CC14) 6 1.33 (br s, 12 H), 3.40 (d, J = 5 Hz, 2 H), 3.7-4.4 (m, 5 H). Anal. Calcd for CllH19Br04: C, 44.76; H, 6.49; Br, 27.07. Found: C, 44.91; H, 6.58; Br, 27.41. Synthesis of 1,23,4-Bis-0 -( l-methylethylidene)-5-deoxy-4,5-didehydroxylitol (15). Into a distillation flask were charged 1,2:3,4-bis-0-( l-methylethylidene)-5-bromo-5-deoxyxylitol(23.6 g, 0.80 mol) and pulverized KOH (54 g, 0.96 mol), and the mixture was heated under reduced pressure to distill crude vinyl ether. Fractional distillation gave 15: bp 101-105 "C (15 mm); yield 14.5-15.8 g (85-92%) ; IR (neat) 2990,2940,2880,1680,1380,1220, 1150, 1060 cm-'; 'H NMR (CC14) 6 1.25 (8, 3 H), 1.33 (s,6 H), 1.43 (s, 3 H), 3.50-4.33 (m, 5 H), 4.53 (m, 1 H); mass spectrum, m / e 214. 0-( l-methylethylidene)-5-bromo-5-deoxyxylitol, 87597-70-4.

Reactions of acids with vinylidenexanthenes (or thioxanthenes) 1 and 9methoxy-9-vinylxanthenes (or thioxanthenes) 8 give xanthene-(or thioxanthene-) 9-spiro-1 '-indenes 7. With bromine or sulfuryl chloride they give the corresponding 2'-halogenoxanthene-(or thioxanthene-)9-~piro-1 '-indenes 5. Formation of such derivatives depends on preferential attack of the reagents on allenes 1 to give initially xanthylium (or thioxanthylium) ions 3 which cyclize. One 71 bond of the allenes 1 can be selectively reduced in acid media. Chemical and spectral evidence for these routes are presented.Recently we reported on the cyclization of vinylidenexanthenes (1, Y = 0, R = alkoxy) in acid media which give xanthene-9-spiro-1'-indenes (7, Y = 0) [l]. This cyclization revealed the preferential reactivity of the 71 bond of the involved xanthene residue. We have subsequently investigated reactions of equimolecular quantities of either bromine or sulfuryl chloride with vinylidenexanthenes and thioxanthenes (1, Y = 0 or S, R = alkoxy) in order to have further insight on the behaviour and reactivity of such polyarylallenes towards halogenation.Addition of bromine took place readily with instantaneous development of very deep blue-violet colour instead of the normal discharge of bromine colour. The same colour developed on addition of sulfuryl chloride to 1 ( Y = O or S) in carbon tetrachloride solution. This suggested that heteroatom in this type of compound would be responsible for development of such colour [l] as it may encourage migration of one halogen atom due to concerted electron-shift in 2 with formation of the coloured oxonium derivative 3. On the other hand, addition may take place through an initial cation attack on the activated central carbon atom of 1, rather than free radical addition to give 3 (Y = 0 or S). On heating solutions of 3 (Y = 0 or S, R = alkoxy) ready evolution of hydrogein halide occurred, affording mainly the corresponding 2'-bromo-6'-alkoxy-3'-aryl-xanthene-(or thioxanthene-)9-spiro-1 '-indenes 5 (Y = 0 or S, X = Br, R = alkoxy). When bromine was added to 1 (Y = 0, R = OMe) and the reaction mixture was left 2 h at RT., the deep blue-violet crystals isolated were identified as the tribromide: 4 (Y = 0, X = Br, R = OMe), in addition to the corresponding bromoindene 5. Compound 4 could be formed by addition of some liberated hydrogen bromide to 3. Formation of bro-Oo18-019)3/79/6/ 1872-06$0l.Oo/O 0 1979 Schweizerische Chemische Gesellschaft

Soci6t6 suisse de chiniic, B&le -Societi svizzera di chimica, Basilea Nachdruck verboten -Tous droits r6servds -Printed by Birkhauser AG., Basel Summary. Xanthenyl and thioxanthenyl halides added readily to asymmetric diarylethylenes and their 2-halogeno-derivatives to give after dehydrohalogenation 1, 1-diaryl-2-[xanthen(or thioxanthen)-9-yl]-ethylenes and 1,l-diaryl-2-halogeno-2-[xanthen(or thioxanthen)-9-yl]-ethylenes. The thioxanthcnylethylenes were also obtained by another way,Reactions of these ethylenes with bromine, chlorine or sulfuryl chloride were influenced by the halogen and the nature of the p-substituent.Dehydrohalogenation of the 2-halogenoxanthenyl(or thioxantheny1)ethylenes gave the corresponding 1, 1-diaryl-2-[xanthen(or thioxanthen)-9-ylidene]-ethylenes.We have reported [l]