New Gas-Phase Domino Processes Leading to Benzopyranones and Benzofurans

Abstract

-A new domino approach to flavones by gas phase pyrolysis of -dioxophosphonium ylides containing a 2-methoxyphenyl group is frustrated by unexpected and novel decarbonylation of the intermediate flavon-3-yl radical leading to 2-phenylbenzofuran. Alternative approaches based on dioxolane protection of one carbonyl, or selective elimination in '-dioxo or -oxo-'-thioxo ylides were not successful, but pyrolysis of a -oxo-'-phenylimino ylide did give the required domino reaction leading to a protected benzopyranone in moderate yield.

Gas-phase domino cyclization of phosphonium ylides leading to the total synthesis of Eustifoline D

“…5,6 More recent developments have included the observation of an eight-stage cascade process, 7 the synthesis of thieno [2,3-b]pyridines, 8 and an application of this approach to the formation of benzopyranones. 9 However all these studies have involved O or S as the cyclizing atom and the corresponding process involving cyclization of N to give indoles is much less developed. There is only one report of this process, and it shows that the situation is complicated in the case of Nmethyl ylides by the possibility of N to C transfer of the reactive centre leading to quinoline products rather than the expected Nmethylindoles in some cases.…”

Oxalyl Chloride: A Versatile Reagent in Organic Transformations

“…Transformation of 2‐(2‐hydroxyphenyl)‐2‐oxoacetic acid 183 into ylide 184 was presented using oxalyl chloride. The 2‐(2‐hydroxyphenyl)‐2‐oxoacetyl chloride obtained from the reaction of 2‐(2‐hydroxyphenyl)‐2‐oxoacetic acid 183 with oxalyl chloride in the presence of DMF as the catalyst was treated with benzyltriphenylphosphonium chloride and BuLi to furnish the expected product 184 (Scheme ) …”

The value of 2 J P–CO as a diagnostic parameter for the structure and thermal reactivity of carbonyl-stabilised phosphonium ylides

“…This was prepared using the published method 58 as yellow crystals directly suitable for X-ray diffraction. Data were recorded at 93(2) K on a Rigaku Mercury 70 diffractometer using Mo-Kα radiation and the structures were solved by direct methods and refined using full-matrix least squares analysis The following crystal data were obtained: C 34…”