Flash vacuum pyrolysis over magnesium. Part 1. Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides

Flash vacuum pyrolysis of benzylidene halides, benzotrihalides and aryl halides over magnesium

“…When the substituted benzylidene halides were subjected to FVP over magnesium there was usually complete reaction at 600 C and products accounting for between 56 and 92% overall yield were identified by a combination of NMR and GCMS methods (Scheme 1, Table 1). As expected from our previous studies on benzyl halides [2], the major product in most cases was that of dehalogenative coupling to give the stilbene mainly as the (E)-isomer 2 but accompanied by a smaller amount of the (Z)-isomer 3. In favourable cases the pure (E)-stilbene could be obtained simply by recrystallisation of the solid at the furnace exit from ethanol and this occurred for 2a 2d and 2h while the previously unreported compound 2i was obtained pure by preparative TLC.…”

“…In all cases there were however varying amounts of other products, notably the reduction products: the bibenzyl 4 and the toluene 5. As we noted previously [1], various pieces of evidence point to the involvement of surface-adsorbed organometallic species in these processes but the formation of apparent hydrogen atom abstraction products is consistent with the behaviour observed for benzylic halides [2]. A previous study on atmospheric pressure flow pyrolysis of 1a under nitrogen at temperatures between 430 and 650 C also gave 10-20% yields of 4 and 5 in addition to stilbene 2a as the major product [26].…”

“…The procedure used was based on that reported previously [1,2]. Using the standard apparatus for FVP [14], the required weight of magnesium turnings was placed at the centre of the furnace tube which was loosely packed with glass wool.…”

“…Introduction Some time ago we described the application of flash vacuum pyrolysis (FVP) over a layer of freshly sublimed magnesium on glass wool as a preparatively useful method for dehalogenative coupling of benzyl halides, and the effect of these conditions on a wide range of haloalkanes, -alkenes and -alkynes was also examined [1,2]. The same method was later used in dehalogenation of dichlorophosphines to generate simple alkylphosphinidenes [3] and an arylphosphinidene [4].…”

Decomposition of vinyl ethers by alkalide K−, K+(15-crown-5)2 via organopotassium intermediates

“…¼ 48-49°C/12 mm Hg. Its MS data and 1 H and 13 C NMR spectra (CDCl 3 ) are presented in [22,23], respectively.…”