Cascade synthesis of new tetracyclic heteroaromatic thieno[2,3-b]pyridine-containing ring systems

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

“…3,4 This was later extended to domino cyclization methods leading to tri-and tetracyclic fused ring heterocycles. 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.…”

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

“…Data were recorded at 293(2) K on a Rigaku Mercury 70 diffractometer using Mo-Kα radiation and the structure was solved by direct methods and refined using full-matrix least squares analysis. The following crystal data were obtained: C 20 H 25 OP, M = 312.37, monoclinic space group P2 1 /c; a = 9.905(2), b = 23.109 (5), c = 15.149(3) Å, β = 90.460(6) ˚, V = 3467.6(12) Å 3 , Z = 8, D c = 1.197 g cm -3 , R = 0.073, R W = 0.2075 for 4939 data with I > 2σ(I) and 397 parameters.…”

Flash vacuum pyrolysis of oxo-stabilised phosphonium ylides containing methoxythiophene and methylthiophene groups

“…For some years we have made a detailed study of oxo-stabilised phosphonium ylides as suitable precursors for synthesis of fused ring heterocycles by FVP in a process involving thermal extrusion of Ph 3 PO to form an alkyne, simultaneous radical generation, and then a sequence of domino cyclisation processes leading to tri-, tetraand pentacyclic fused ring aromatic heterocycles. Recent examples showing the versatility of the method include pyrolysis of nearly 40 compounds of structure 1 to give the corresponding products 2 (Scheme 1) including representatives of 24 different heterocyclic ring systems [3], cascade processes of up to eight steps [4], and introduction of nitrogen, either by starting from pyridine-containing ylides 3 which react to afford 4 [5], or by using a nitrogen-based cyclising radical which unexpectedly leads to both five-and six-membered ring heterocycles as illustrated by pyrolysis of ylide 5 to give both the quinoline 6 and the furocarbazole natural product Eustifoline D 7 [6][7][8]. In terms of the mechanism of these processes, this is illustrated for the case of a generalised ylide in Scheme 2 and is supported by the results of isotopic labelling [9].…”