Vapour phase pyrolysis of benzoxazinones

La formation de biphénylènes par pyrolyse de mélanges de précurseurs de benzynes

“…On trouve dans la IittCrature d'autres prtparations de biphCnyl6nes par pyrolyse de composCs prCcurseurs de benzyne ou du diradical-2,2' biphenyle (16)(17)(18)(19)(20)(21). Par exemple, la pyrolyse du dioxyde-1,l de mCthyl-5 benzothiadiazole (9) conduit a la formation des dimithyl-2,6 (10) et dimCthyl-2,7 (11) biphtnylines (17), [3].…”

Cyclobuta[1,2-c:3,4-c′]dithiophene

“…spectrum of (1) resembles that of biphenylene, but shows a pronounced hypsochromic shift. A smaller effect has been observed in the spectrum of benzo [3,4]cyclobuta-[ 1,2-c]thiophene.g This, in conjunction with the high-field shift of the 1H n.m.r. spectrum, provides convincing evidence for conjugation between the two thiophene rings, and the associated presence of a paramagnetic current in the central cyclobutadienoid ring.…”

“…spectrum suggested some interaction between the two heterocyclic rings. Benzo [3,4]cyclobuta[ 1,241thiophene6 and a derivative7 have recently been prepared by flash vacuum thermolysis; this method is here extended to the synthesis of the title compound Nitration of 3-iodothiophene-Zcarbaldehyde (H2SO4, HN03, CH2C12; 0 "C) gave the 4-nitro derivative (3),7 m.p. 120-121 "C (37%); bH (CDC13) 8.76 (5-H, d) and 9.94 (CHO, d), J 1.5 Hz.…”

3,4-Didehydrothiophene: Generation, Trapping Reactions, and Ab Initio Study1

“…Although both 2,3-didehydrothiophene ( 1 ) and 3,4-didehydrothiophene ( 2 ) had been suggested as reactive intermediates by Wittig in the early 1960s, the validity of such claims was later questioned. 7bc, Subsequently, hetaryne 1 was generated from thiophene-2,3-dicarboxylic anhydride and accordingly trapped . Evidence for the existence of 2 has surprisingly never been obtained despite many experimental attempts. 12c, Inspired by the recent generation of benzyne from (phenyl)[ o -(trimethylsilyl)phenyl]iodonium triflate, we report herein unequivocal verification of 2 as an intermediate. It is believed that the five-membered 2 is the smallest cyclic cumulene ever characterized.…”

“…In other Diels−Alder reactions, furan, 2-methylfuran, and 2,5-dimethylfuran were all found to react readily with 2 to furnish adducts 8a , 8b , and 8c , in 31%, 17%, and 13% yields, respectively . It appeared that 2 did not dimerize to provide 2,5-dithiabisnorbiphenylene, , even for the condition in which no trapping reagent was involved.

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