Search results for "Flash vacuum pyrolysis"
showing 10 items of 11 documents
Benzoxetes and Benzothietes ¾ Heterocyclic Analogues of Benzocyclobutene
2012
Benzo-condensed four-ring heterocycles, such as benzoxetes 1 and benzothietes 3 represent multi-purpose starting compounds for the preparation of various higher heterocyclic ring systems. The thermal or photochemical valence isomerizations between the benzenoid forms 1,3 and the higher reactive o-quinoid structures 2,4 provide the basis for the synthetic applications. On the other hand, this valence isomerization impedes in particular the generation and storage of 1 because the thermal equilibrium 1 ⇆ 2 is completely on the side of 2. Thus, the number of erroneous or questionable benzoxete structures published to date is surprisingly high. On the contrary, the thermal equilibrium 3 ⇆ 4 is o…
Gas-phase detection of HSOH: synthesis by flash vacuum pyrolysis of di-tert-butyl sulfoxide and rotational-torsional spectrum.
2003
Gas-phase oxadisulfane (HSOH), the missing link between the well-known molecules hydrogen peroxide (HOOH) and disulfane (HSSH), was synthesized by flash vacuum pyrolysis of di-tert-butyl sulfoxide. Using mass spectrometry, the pyrolysis conditions have been optimized towards formation of HSOH. Microwave spectroscopic investigation of the pyrolysis products allowed-assisted by high-level quantum-chemical calculations--the first measurement of the rotational-torsional spectrum of HSOH. In total, we have measured approximately 600 lines of the rotational-torsional spectrum in the frequency range from 64 GHz to 1.9 THz and assigned some 470 of these to the rotational-torsional spectrum of HSOH …
1H-naphtho[2,1-b]thiete and 2H-naphtho[2,3-b]thiete- synthesis and reactivity
1994
Abstract The title compounds 4 and 8 are obtained by flash vacuum pyrolysis of the corresponding hydroxymethylthionaphthols 3 and 7. Whereas 4 shows a smooth ring opening on heating, 8 is thermally stable but reacts photochemically. The different behavior is explained on the basis of an MNDO calculation. The valence isomers 4′ and 8′ represent thioquinonemethides, which are highly reactive components in [12π + 2π]cycloaddition processes (4 → 9, 10, 11; 8 → 12).
ChemInform Abstract: 1H-Naphtho(2,1-b)thiete and 2H-Naphtho(2,3-b)thiete - Synthesis and Reactivity.
2010
Abstract The title compounds 4 and 8 are obtained by flash vacuum pyrolysis of the corresponding hydroxymethylthionaphthols 3 and 7. Whereas 4 shows a smooth ring opening on heating, 8 is thermally stable but reacts photochemically. The different behavior is explained on the basis of an MNDO calculation. The valence isomers 4′ and 8′ represent thioquinonemethides, which are highly reactive components in [12π + 2π]cycloaddition processes (4 → 9, 10, 11; 8 → 12).
Naphthothiete und ihre Anwendung in der Heterocyclen-Synthese
1995
Naphtothietes and Their Application to the Synthesis of Heterocycles The three isomeric naphthothietes 5, 11, and 16 were prepared according to the reaction sequences shown in Schemes 1–3. The final step was in each case a flash vacuum pyrolysis (FVP) of the corresponding mercaptonaphthalenemethanol 4, 9, and 15, respectively. The thiete rings in 5 and 11 can be opened by gentle heating; the ring opening of the isomer 16 possesses a much higher activation barrier. A MNDO calculation of the ΔHf values of 5, 11, and 16 and the open isomers 5′, 11′, and 16′ provides an explanation for the different behavior. Photochemical ring opening represents a useful alternative. The reaction Schemes 4, 6,…
Generation and transformation of the [3.3.1]propellane skeleton by thermal rearrangements
1994
Abstract In a sequence of unexpected thermal rearrangements the strained monocyclic alkyne 4 is transformed into the tricyclic system 5 which yields in a flash vacuum pyrolysis again a monocyclic compound 10 .
Thermal Rearrangements of Perchlorohexatrienes-Structures and Experimental and Theoretical Evaluation of Pathways to Isomerization and Cyclization
2009
We have prepared trans- (1) and cis-octachloro-1,3,5-hexatriene (2) by known routes and studied their thermal behavior experimentally and theoretically by ab initio calculations. The three double bonds in 1 and 2 are completely decoupled due to steric hindrance by the eight Cls, as indicated by calculations as well as the single-crystal X-ray structure of 1. The cis isomer 2 can be isomerized to the trans isomer 1 by heating it to 220–250 °C either neat or dissolved in high-boiling solvents, leading to a roughly 2:1 mixture of trans and cis isomers. Calculations at several different levels of theory predict 1 and 2 to be isoenergetic within 2 kJ mol–1. Unimolecular cis/trans isomerization i…
ChemInform Abstract: Benzoxetes and Benzothietes - Heterocyclic Analogues of Benzocyclobutene
2012
Benzo-condensed four-ring heterocycles, such as benzoxetes 1 and benzothietes 3 represent multi-purpose starting compounds for the preparation of various higher heterocyclic ring systems. The thermal or photochemical valence isomerizations between the benzenoid forms 1,3 and the higher reactive o-quinoid structures 2,4 provide the basis for the synthetic applications. On the other hand, this valence isomerization impedes in particular the generation and storage of 1 because the thermal equilibrium 1 2 is completely on the side of 2. Thus, the number of erroneous or questionable benzoxete structures published to date is surprisingly high. On the contrary, the thermal equilibrium 3 4 is on th…
An alternative route to 2H-naphtho[1,2-b]thiete and its cycloaddition products
1998
2-(1H-Benzotriazol-1-ylmethyl)-1-naphthalenol (1) can be transformed in high yields to the corresponding thiol 4. Flash vacuum pyrolysis of 4 leads to 2H-naphtho[1,2-b]thiete (5). The benzotriazolyl group proved to be a good leaving group; however, a subsequent nitrogen extrusion takes place under flash vacuum pyrolysis conditions and cyclopentadienecarbonitriles 6a,b are formed by a ring contraction (Scheme 1). Cycloaddition reactions of 5 and dienophiles or heterodienophiles yield the naphtho-condensed sulfur heterocycles 8, 10, 12 and 14 (Scheme 2).
Thermal rearrangements of 1,2-dialkoxybenzenes by flash vacuum pyrolysis
1995
Flash vacuum pyrolysis of 1,2-dialkoxybenzenes 1a-c leads to the liberation of alkanes from the interacting side chains. A rearrangement of the skeleton yields the o-hydroxy carbonyl compounds 2 and 4. The generation of phenol 3 can be rationalized by a decarbonylation. The latter reaction is the sole process which can be observed for the bicyclic starting compound 9.