Flash vacuum pyrolysis FVP

The mechanism of this reaction has not been thoroughly explored. Some work has been done in analysis of potential intermediates for the reaction, although these intermediates were generated using flash vacuum pyrolysis (FVP). Materials in this experiment were trapped and IR spectrum suggested the formation of a ketene prior to cyclization. 

The 5-substituted 1,3-dioxolan-4-one 23 is readily deprotonated at the 5 position and can be alkylated with a variety of alkyl halides. The resulting products 24 decompose upon flash vacuum pyrolysis (FVP) at 600°C with loss of acetone... 

In contrast, flash-vacuum pyrolysis (FVP)155 or spray-vacuum pyrolysis (SVP)154 of the homologous phenethyl azidoformates yield, in every instance except for the 4-cyano and 4-nitro-derivatives, the thermally stable [1,3]oxazino[3,4-a]azepines 9 accompanied by lesser amounts of the oxazolidinones 10, formed by nitrene insertion at the benzylic carbon center. 

The first and to date only synthesis of the parent system 2 uses a flash-vacuum pyrolysis (FVP) of 7,8-diazapentacyclo[4.2.2.02-5.03 9.04 10]dec-7-ene (diazabasketene, 1). After condensation at -196 °C, the pyrolysis product is distilled in vacuum to give pure azocine in ca. 60% yield.12... 

The combination of the flash vacuum pyrolysis (FVP) technique169 with mass spectrometry proved to be particularly useful in identification and characterization of both the fragmentation/rearrangement patterns, intermediates and/or final products formed (see Section IV.E.l). Usually, no structures are indicated in the mass spectra, although ionization and appearance potential can, in principle, provide structural information. 

Phosphorus ylids are quite common (see 16-47) and keto-phosphorus ylids (RCOCH=PPh3) are also known. When these compounds are heating (flash vacuum pyrolysis, FVP) to great than >500°C, alkynes are formed. Simple alkynes can... 

Savignac et al. [26] excellently reviewed this topic, but Aitken and coworkers investigated further the flash vacuum pyrolysis (FVP) of the )0-oxophosphorus ylides (Scheme 5). 

Barton and co-workers" performed flash vacuum pyrolysis (FVP) on trimethyl-silylvinylmethylchlorosilane (30), resulting in the production of trimethylchlorosi-lane (30%), trimethylvinylsilane (11.5%), and most interestingly, ethynylmethyl-silane (34, 11.9%). A proposed mechanism for the synthesis of 34 (Scheme 10) begins with the lo.ss of trimethylchlorosilane to form silylene 31, which can rearrange either to silaallene 32 or to silirene 33, both of which can lead to the isolated ethynylsilane. 

For example, McNab and coworkers have discovered that flash-vacuum pyrolysis (FVP) (1000 °C, 0.01 Torr) of pyrrole 10-114 led to the formation of pyrrolo[2,l-a]isoindol-5-one 10-117 in 79% (Scheme 10.29) [44]. The transformation is proposed to proceed via an initial 1,5-aryl shift to give intermediate 10-115, which then undergoes an elimination of methanol. Finally, electrocydization of the ketene 10-116 results in the formation of 10-117. 

Flash vacuum pyrolysis (FVP) of the 3-(iV-(pyrimidin-2-yl)imino-l-morpholino)propanoate 179 led to pyrimido-pytimidines 182 and 184, as a result of competition between thermal loss of ethanol or morpholine. The ketenimine 181, being unable to undergo cyclization, underwent [l,3]-ethoxy migration to form 183, leading to 184 (Scheme 28). The ratio of the products was studied on variation of the temperature (400, 530, and 600 °C) and the nature of the amino substiuent (NR1R2 = morpholino, pyrrolidino, N(Me)Ph ) <2004AJC577>. 

Pederson and co-workers investigated the thermal behavior of 1,6,6aA4-trithiapentalene and some methyl-substituted derivatives using flash vacuum pyrolysis (FVP). The main products of the fragmentation, following loss of CS and/or CH2=C=S, were shown to be thiophene-3-thiones, or the thiol tautomers <1997J(P2)1261>. 

FVP-gas electron diffraction (FVP-GED), 21 139. See also Flash vacuum pyrolysis (FVP)... 

The decisive break came in 1991 when Scott and co-workers reported the formation of corannulene from 7,10-diethynylfluoranthene 19 under flash vacuum pyrolysis (FVP) conditions. The critical features of this approach appear to be the high temperature employed (900-1000 °C) and the gas-phase conditions. The high temperature provides energy for drastic fluctuations in 8 away from its equilibrium geometry, allowing the reactive centers to come close enough to form the new bonds while the gas-phase conditions prevent polymerization (although some polymeri-... 

The second approach is based on the idea of synthesizing bowl-shaped hydrocarbons in which curved networks of trigonal C-atoms map out the same patterns of five- and six-membered rings as those found on the surfaces of Cjq and/or the higher fullerenes [145-152]. An example for such an open geodesic polyarene is circum-trindene (5), generated by flash-vacuum pyrolysis (FVP) of trichlorodecacyclene 4 (Scheme 1.5) [152], Circumtrindene represents 60% of the framework of Cjq. 

Flash vacuum pyrolysis (FVP) represents a special method for inducing decomposition of thietane compounds. Block et al. succeeded for the first time in the preparation of methylene sulfine in the gas phase, applying this method to thietane 1-oxide. The reaction starting at 600°C was followed by mass and microwave spectroscopy. 

Flash vacuum pyrolysis (FVP) of the tetrahydro-l,3-oxazine derivative 171, derived from the condensation of spiro-oxazine 170 and methoxymethylene-substituted Meldmm acid, resulted in formation of pyrrolo[l,2-r ][l,3]oxazine 172, which in (CD3)2CO at —20°C proved to be a 47 53 mixture of the keto (A) and enol (B) tautomers (Scheme 28) <2002J(P1)548>. 

The first example of the direct observation of a thermally generated nitrile ylide has been reported (3). This was achieved by studying the thermal flash vacuum pyrolysis (FVP) decomposition of the oxazaphospholes 3 (R = t-Bu, Ph) via the... 

A convenient method for generating and trapping reactive ketenes is the flash-vacuum pyrolysis (FVP) of substituted Meldrum s acid derivatives. The dispirocyclobutane-l,3-dione 9 is obtained from the transient ketene 8 generated by FVP of the diester precursor 7.56... 

Head-to-tail intramolecular dimerization of nonactivated vinyl groups can also occur in compounds in which the tether is only two atoms long under conditions of flash-vacuum pyrolysis (FVP). Under such conditions strained bridged polycyclic derivatives can be prepared.78 The formation of 18 is the result of intramolecular head-to-tail cycloaddition of the Cope rearrangement intermediate derived from 1,2-divinylacenaphthene.78... 

Flash vacuum pyrolysis (FVP) of 1,3-dithiolane 1-oxides (88-90), as a possible route to thiocarbonyl compounds, has been studied.57 Thiobenzophenone and thiofenchone are obtained from (88) and (89), respectively, but there was no evidence of heptane-4-thione formation from (90). A stepwise homolytic cleavage has been proposed. 

The flash vacuum pyrolysis (FVP) of 1-allyl-l-methyl-l-silacyclopent-3-ene gives rise to elimination of propene and formation of silole 3 identified as its dimer 5, and by its Diels-Alder adducts with maleic anhydride and hexafluorobutyne. However, the silole 3 has been detected as a monomer by the MS-FVP technique6. 

Thioformyl and thiocarbonyl cyanides. The long-sought for IR spectrum of this compound was obtained by Wentrup and coworkers162. S=CH—CN was prepared by Flash Vacuum Pyrolysis (FVP) of allyl cyanomethyl sulfide and condensed in an argon matrix. The absorption frequencies(in cm-1) and the intensities (in km mol-1) corresponding to the five bands observed were V2, CN stretch (2221, 17) vj, CH rock (1320, 11) U4, CS stretch (1103, 10) 05, CC stretch (889, 8) vg, CH wag (824, 26). These assignments were made on the basis of MP2/6-31G(d) calculations. The spectrum of formyl cyanide is reported and discussed elsewhere163. 

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