Synthesis of the 2H‐1‐Thiacyclobutabenzene System

Abstract

Thiete ( I ) and its simple derivatives are labile compounds at room temperatureand tend to polymerize"'. Their 1,l-dioxides (2)Lz1 are considerably more stable and better to handle. Stabilization is also possible by incorporation of the double bond of the system in an annelated benzene ring.( 1 ) ( 2 ) We succeeded in synthesizing the first heterocycle of the type 2H-1 -thiacyclobutabenzene (2H-1 -benzothiete) by photo-The photochemical primary step affords the carbene ( 4 ) , which subsequently rearranges to the ketene (6). Addition ofmethanol to (6) leads to the methyl 2H-1-benzothiete-2-carboxylate (7) (b.p. 73 T/0.06 torr, yield 30 %). An alternative reaction which ( 4 ) might undergo is insertion into the 0-H bond of the methanol with formation of the 3-methoxy-2-0~0-2,3-dihydrobenzo[b]thiophene (5)r31. For confirmation of the structure of (7) we have prepared (S), m.p. 50°C, in 40% yield cia an independent route by acid-catalyzed decomposition of ( 3 ) . (41 H (51In contrast to the corresponding aza compounds ( 5 ) cannot be obtained by photolysis of (3)14].For the spectroscopic characterization of (7) a comparison with (5) and (3) is useful. The C O stretching vibration in the IR spectrum of (3) appears-as is usual for a-diazo carbonyl compounds-at low wave numbers (in KBr: 1640 cm ~ I). In the thiolactone ( 5 ) the absorption is shifted to 1705cm-', and in (7) it reaches the normal value of 1740 cm -' for saturated aliphatic esters.The 'H-NMR spectrum of ( 5 ) recorded in CDC13 shows one singlet for the tertiary hydrogen at 6 = 5.0 ppm and one for the methyl protons at 6=3.5ppm. In the case of the ester (7) both signals are shifted to lower field strengths (5.2 and 3.8 ppm, respectively). Especially informative are the I3C-NMR spectra. The carbonyl carbon and the carbon atom adjacent to it give a marked high field shift of ca. 35ppm on going from ( 5 ) through ( 3 ) to (7) (6=203.1, 186.4 and 169.4ppm, 6=85.1, 70.6, and 49.2, respectively; in CDC13, TMS internal)[51. The resonance of the methyl C-atom in ( 5 ) lies at lower field strength than that of (7) (6=56.7 and 52.8 ppm, respectively).[**I This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.In contrast to (3) and ( 5 ) the bicyclic fundamental structural unit of (7) is considerably more stable towards fragmentation in the mass spectrometer.We attribute the greater thermal stability of (7) over ( I ) to the fact that the ring opening ( 7 ) -+ ( 8 ) is very much less energetically favorable than that of (1) + (9). ' Received: December 12, 1975 [Z 362 IE] German version: Angew. Chem. XX. 94 (1976) CAS Registry numbers:

Computer-Assisted Mechanistic Evaluation of Organic Reactions. 24. Carbene Chemistry

“…groups,87 conforming well to the observation that the reaction proceeds poorly except in cyclic systems, wherein the requisite conformation is imposed (eq 19, a sulfur analog),88 and diazomethylketones (eq 20, top route),89 in which the absence of a second alkyl substituent would make the necessary conformation attainable.…”

Benzazetidines and Related Compounds: Synthesis and Potential

“…Benzofuranone 16 and the o ‐hydroxyphenyldiazomethane 17 can be converted, through liberation of carbon monoxide and nitrogen, respectively, to benzoxete 18 either by irradiation and by flash vacuum pyrolysis . The first successful synthesis of a benzothiete was accomplished by Wolff rearrangement of 3‐diazobenzo[ b ]thiophen‐2(3 H )‐one ( 19 ), which under irradiation generates ketene 20 . This intermediate can be easily trapped with alcohols, leading to esters 21 b .…”

Synthesis of Three‐Membered and Four‐Membered Heterocycles with the Assistance of Photochemical Reactions

“…Meier et al . first time in 1976 generated benzothietes successfully. The ketene was formed by Wolff rearrangement of 3‐diazobenzo[ b ]thiophen‐2(3 H )‐one.…”