Flash vacuum thermolysis conditions

Keywords retro-Diels-Alder reaction under flash vacuum thermolysis conditions... 

Professor Stanislaw Lesniak was born in 1952 in Gorlice (Poland). He obtained his M.Sc. degree in chemistry from the University of Lodz (Poland) in 1976, studying the reactivity of aziridines. He received his Ph.D. in chemistry from the same university in 1983 for study of stereoselective reduction of aziridinyl ketones. He presented his habilitation thesis at the University of Lodz in 1996. Professor Lesniak lectured at the University of Lodz from 1977 and six months at the University Claude-Bernard Lyon 1 in 1987/1988. He was a research fellow in the Department of Chemistry at the University Claude-Bernard Lyon 1 in a group of Prof. Andre Laurent in 1984-85, 1987-1988, and 1991-92. At the same university, he was employed as a CNRS research worker in 2001-02 in the group of Prof. P. Goekjian. The focus of his studies has been synthesis and reactivity of small molecules, radical reactions, and reactions under flash vacuum thermolysis conditions. 

Under flash vacuum thermolysis conditions (SSO-600 C/0.01 mmHg), even an acetoxy group can be induced to rotate inward, as shown by the conversion of (30) to the ketoaldehyde (31). The presence of a suitably placed dienoj ile, even the weak terminal vinyl group as in (30a), results only in the intramolecular Diels-Alderjnoduct (32), thereby demonstrating the large preference for outward motion by an acyloxy derivative." Similar thermolysis of 1-acetoxy-l-methylbenzocyclobutene (30 R = = Me)... 

The retro-Diels-Alder reaction has found considerable use in the preparation of reactive molecules and intermediates, particularly under flash vacuum thermolysis conditions.Application of this methodology to the adducts (85) of arynes and various dienes (Section II.2.B.b) does not generally regenerate the aryne and the diene but either gives the isobenzo derivative 86 and an alkyne by an alternate retro-Diels-Alder reaction, or... 

Unstabilized conjugated cycloalkenethiones of ring size 5-7 [(48a-c), respectively] have been synthesized by retro-ene reaction of the corresponding cycloalkenyl (or propargyl) sulfides (47) under flash vacuum thermolysis conditions. ... 

Retro-ene reaction of an N-allylsilanamine under flash vacuum thermolysis (FVT) conditions. The iminosilane has been identified not only by reaction with the trapping agent /-butyl alcohol, but also directly by coupling the oven with a high-resolution mass spectrometer.7... 

Retro Diels-Alder reactions often require severe conditions, high temperatures, and, sometimes, flash vacuum thermolysis. Microwave irradiation has been used as an alternative to these harsh conditions [12], even using graphite as a support [45]. Similarly, the use of higher input power has enabled retro-Diels-Alder reactions of anthracene derivatives to occur in 3-5 min [41]. This method is an alternative to the use of flash thermolysis. The use of graphite is a prerequisite for obtaining high temperatures in a short time. 

The major fragmentation in mass spectra of 1,2,5-oxadiazoles is attributed to the loss of nitrile and nitrile oxide or expulsion of NO. The conversion of 3,4-dicyano-l,2,5-oxadiazole-2-oxide (3,4-dicyanofuroxan) 10 to cyanogen iV-oxide 11 (Equation 5) was investigated under the conditions of collisional activation (CA) and neutralization-reionization (NR) mass spectrometry. Flash vacuum thermolysis mass-spectrometry (FVT-MS) and flash vacuum thermolysis infra-red (FVT-IR) investigations of furoxans 10, 12, and 13 reveal that small amounts of cyano isocyanate accompany the formation of the main thermolysis product 11 <2000J(P2)473>. 

The thermolytic preparation by De Shong et al. (74) of azomethine ylides from aziridines and their intermolecular reactions are the first examples of singly stabilized ylides of this type. However, the protocol has been further extended to include intramolecular processes. Aziridines tethered to both activated and unactivated alkenes were subjected to flash vacuum thermolysis generating cycloadducts in moderate-to-excellent yields. While previously singly activated alkenes had furnished low material yields via an intermolecular process, the intramolecular analogue represents a major improvement. Typically, treatment of 222 under standard conditions led to the formation of 223 in 80% yield as a single cis isomer. Similarly, the cis precursor furnished adduct 224 in 52% yield, although as a 1 1 diastereomeric mixture (Scheme 3.77). 

On submitting D-isomannide 2,5-dinitrate (15) to flash vacuum thermolysis, 1,4 3,6-dianhydro-D-mannopyranose (145) was obtained as the main product (75 - 80% yield), accompanied by 5 -10% of the monoketone 8a. In contrast, when D-isosorbide 2,5-dinitrate (14) was treated under the same conditions, a 6 3 1 mixture consisting217 of 8a, 145, and its D-gluco epimer 146 resulted (see Scheme 40). These results could be explained by a restricted number of rearrangements of intermediate radicals, with inversion or retention of configuration, respectively. By reduction with sodium borohydride, 8a was stereoselectively converted into D-isomannide (4). 

Flash vacuum thermolysis (FVT) of 9-azidophenanthrene, 6-(5-tetrazolyl)phenan-thridine, and [l,2,3]triazolo[l,5-/]phenanthridine give 9-cyanofluorene as the principal product and 4-cyanofluorene as a minor product.74 A nitrene intermediate was detected by ESR in the case of 9-azidophenanthrene a carbene intermediate was detected from the other two starting materials. DFT calculations were applied to examine other potential reaction products and it was concluded that although the observed products are not the kinetically favoured products, they are the thermodynamic sink and cannot be avoided under FVT conditions. 

The results of a study of the flash vacuum thermolysis (FVT) of 2-(5-tetrazolyl)quinoline and l-(5-tetrazolyl)iso-quinoline 176 have been summarized <2004JOC2033>. By various methods, in particular, by 13C labeling experiment with l-(5-tetrazolyl-5 13C) isoquinoline 176, the tetrazole ring was shown to lose two nitrogen molecules under FVT conditions furnishing carbene 177. Carbene 177 at 400 °C affords 2-aminonaphthalene 179 and other compounds (not shown in the scheme) expected from 2-naphthylnitrene 178 (Scheme 12) <2004JOC2033>. 

A novel synthesis of a-unsaturated sulfines has been introduced by Bra-verman et al. [99]. Et3N or DABCO treatment of allylic and benzylic tri-chloromethyl sulfoxides triggered the elimination of chloroform and formation of the sulfines. It must be stressed that these sulfines are thermally relatively stable, and this stands in high contrast to the corresponding thio-carbonyl compounds unsaturated thioaldehydes cannot be monitored under the same experimental conditions and have to be used at very low temperature or trapped in situ. The first synthesis of thioacrolein S-oxide was achieved by flash vacuum thermolysis of an anthracene allyl sulfoxide [100], and both isomers in a (Z E) ratio of 78 22 were characterised by NMR spectroscopy at -60 °C. 

In the conditions of flash vacuum thermolysis (FVT), germoles 77 are decomposed with the final formation of germaisonitriles such as 78 <19990M5322> which are characterized in the gas phase by photoelectron spectroscopy. 

P-benzoquinone, 62, loses CO in two successive steps under conditions of flash-vacuum thermolysis. The thermal decomposition is precisely analogous to the fragmentation of the molecule ion in a mass spectro-... 

Possessing the SCCCS fragment, this binary compound could presumably be a source for the generation of carbon subsulfide, C3S2, under the conditions of flash vacuum thermolysis. 

Retro-Diels-Alder reactions often require drastic conditions, high temperature and sometimes even flash-vacuum thermolysis (FVT). Such thermolytic procedures have been used to prepare unsaturated amino alcohols from a variety of amino alcohols. Several reactions were performed for a variety of neat liquid adducts and submitted to MW irradiation or to classical heating at the same temperature. The improvements obtained by coupling MW and the solvent-free technique are remarkable if we consider that both classical thermolysis and FVT (leading to decomposition) are poorly productive (Scheme 31). 

Perhaps flash vacuum thermolysis of 342 should be tried, for the 2-furyl-carbenes derived from 343 do give ring-opened acetylenes (344-345) in 20-60% yields under such conditions (Eq. 98).381... 

Flash vacuum thermolysis (FVT) was applied to (1) in order to prevent intermolecular reactions, when it was found that (1) was readily thermolyzed to an alkyne, a nitrile, and nitrogen in high yields (Equations (5) and (6)). This tends to suggest that 1,2,3-triazine has only weak aromaticity, since pyridine and pyridazine rings are stable under the same conditions. Two sets of products were... 

Rearrangements of aromatic and heteroaromatic nitrenes can be initiated with either heat or light. The thermal reaction is typically induced by flash vacuum thermolysis, with isolation of the products at low temperatures. Photochemical experiments are conducted either under matrix isolation conditions or in solution at ambient temperature. These rearrangements are usually initiated by ring expansion of the nitrene to a seven-membered ring ketenimine or carbodiimide (i.e., an azacycloheptatetraene). 

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