Tetrahedron p. 6311 - 6318 (1998)
Update date:2022-08-04
Topics: Crystallization Purification Drying Add thiosemicarbazide to the solution. Typically, a 1 Formation of 3-AP
Niu, Chuansheng
Li, Jun
Doyle, Terrence W.
Chen, Shu-Hui
Palladium-catalyzed cross-coupling of methylboronic acid with 2-chloro- 3-nitropyridine produced 2-methyl-3-nitropyridine 4 in one step in high yield. Oxidation of 4 with selenium dioxide gave aldehyde 5. Alternatively, condensation of 4 with DMFDMA followed by oxidation gave 5 in a two step higher yielding conversion. Subsequent direct coupling of 5 with thiosemicarbazide followed by reduction of the nitro group using stannous chloride or sodium sulfide provided 3-AP (3). Reduction with sodium hydrosulfite gave 3-HAP (8). Finally a route which avoids the reduction of a nitro function was devised. Thus direct coupling of styrene with 2-chloro-3- aminopyridine 9 under Heck reaction conditions gave 16 which was converted to 17, oxidized to the aldehyde 18 and converted to 3-AP (3) with in situ deblocking of the t-Boc functionality.
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