A radical mediated approach to the core structure of huperzine A
摘要:
The synthesis of the core structure of huperzine A by cyclisation of 2-pyridylmethyl radicals is described. (2-Methylpyridin-3-yl)cyclohexenols are directly selenated at the benzylic position by deprotonation/selenation and the products undergo either 5-exo-trig or 6-exo-trig radical cyclisations giving access to hexahydroindenopyridines and the bicyclo[3.3.1]nonane core of huperzine A, respectively. (c) 2005 Elsevier Ltd. All rights reserved.
Selective bromination of 2-methoxy-6-methylpyridine 2 afforded 5-bromo-2-methoxy-6-methylpyridine 8. Deprotonation of this pyridine derivative in benzylic position or lithium-bromine exchange allowed the regio-selective introduction of various electrophiles.
Synthesis of the Bicyclo[3.3.1]nonane Core of Huperzine A and Novel Pyridine-Fused Tricycles by Cyclisation of Pyridine-Based Radicals
作者:Vittorio Caprio、Jarrod Ward
DOI:10.3987/com-08-s(d)48
日期:——
The cyclisation of 3-pyridyl radicals and (2-pyridyl)methyl radicals, generated from (pyridyl)cyclohexenols 5 to 8, has been examined as part of a model study directed towards the synthesis of huperzine A. The 3-pyridyl radical, generated from 3-bromopyridine 5, undergoes 5-exo-trig cyclisation to give hexahydroindenopyridine 10. Related pyridine-fused tricycle 12 is formed by 5-exo-trig cyclization of the (2-pyridyl)methyl radical derived from selenide 7b, while the radicals generated from selenides 8b and 19 undergo 6-exo-trig cyclisation to give the bicyclo[3.3.1]nonane core of huperzine A.