Health & Environmental Research Online (HERO)


Print Feedback Export to File
5311017 
Journal Article 
Flash vacuum pyrolysis of stabilised phosphorus ylides .10. Generation of 2-methylstyrylalkynes and their thermal cyclisation to 2-alkenylnaphthalenes 
Aitken, RA; Boeters, C; Morrison, JJ 
1997 
Journal of the Chemical Society, Perkin Transactions 1
ISSN: 1472-7781
EISSN: 1364-5463 
17 
2625-2631 
WOS:A1997XW07800026 
A series of nine 2-methylcinnamoyl phosphorus ylides 7 have been prepared and are found upon FVP at 500°C to undergo loss of Ph3PO to afford the corresponding styrylalkynes 8 whose fully assigned 13C NMR spectra are presented. FVP of the ylides at 900°C leads to cyclisation to give substituted naphthalenes 9-18; the mechanism of these reactions may proceed either by initial hydrogen atom loss or an initial [1,7]hydrogen shift, but an alternative route involving an initial [1,3]hydrogen shift has been ruled out by examination of a deuterium labelled analogue. For the α-phenyl ylides 7d and 7i a further cyclisation leads to benzo[c]fluorene derivatives and this process has been extended to a thiophene analogue to give fluoreno[3,4-b]thiophene. The formation of 2-ethylnaphthalene as the main product from the α-methoxycarbonyl ylide 7e is due to a secondary thermal reaction of methyl 2-naphthylacetate which may involve a radical chain reaction featuring, as the propagation step, an unusual homolytic substitution at a methoxy carbon by a 2-naphthylmethyl radical.