4-Penten-2-OL → 4E-N-methyl-5-(5-methoxy-3-pyridyl)-4-penten-2ol

Participants

Reaction Conditions

Reaction Steps

In another embodiment, a compound such as (4E)-N-methyl-5-(5-methoxy-3-pyridinyl)-4-penten-2-amine can be synthesized by coupling a halo-substituted pyridine, 5-bromo-3-methoxypyridine with an olefin containing a secondary alcohol functionality, 4-penten-2-ol, under Heck reaction conditions; and the resulting pyridinyl alcohol intermediate can be converted to its p-toluenesulfonate ester, followed by treatment with methylamine. Typically, the types of procedures set forth in W. C. Frank et al., J. Org. Chem. 43: 2947 (1978) and N. J. Malek et al., J. Org. Chem. 47: 5395 (1982) involving a palladium-catalyzed coupling of an olefin and an aromatic halide are used. The halo-substituted pyridine, 5-bromo-3-methoxypyridine is synthesized using methodology similar to that described by H. J. den Hertog et al., Recl. Trav. Chim. Pays-Bas 67:377 (1948), namely by heating 3,5-dibromopyridine with 2.5 molar equivalents of sodium methoxide in dry methanol in the presence of copper powder (5%, w/w of the 3,5-dibromopyridine) in a sealed glass tube at 150° C. for 14 hours to produce 5-bromo-3-methoxypyridine. The resulting 5-bromo-3-methoxypyridine, previously described by D. L. Comins, et al., J. Org. Chem. 55: 69 (1990), can be coupled with 4-penten-2-ol in acetonitrile-triethylamine (1:1:1, v/v) using a catalyst consisting of 1 mole % palladium(II) acetate and 4 mole % tri-o-tolylphosphine. The reaction is carried out by heating the components in a sealed glass tube at 140° C. for 14 hours to yield (4E)-N-methyl-5-(5-methoxy-3-pyridinyl)-4-penten-2-ol. The resulting alcohol is treated with 2 molar equivalents of p-toluenesulfonyl chloride in dry pyridine at 0° C. to produce (4E)-N-methyl-5-(5-methoxy-3-pyridinyl)-4-penten-2-ol p-toluensulfonate. The tosylate intermediate is treated with 120-molar equivalents of methylamine as a 40% aqueous solution, containing a small amount of ethanol as a co-solvent to produce (4E)-N-methyl-5-(5-methoxy-3-pyridinyl)-4-penten-2-amine. When 3,5-dibromopyridine is submitted to Heck coupling with N-methyl-N-(tert-butoxycarbonyl)-4-penten-2-amine, under conditions described above, N-methyl-N-(tert-butoxycarbonyl)-5-(5-bromo-3-pyridinyl)-4-penten-2-amine is produced. This can be coupled in a subsequent Heck reaction with styrene and deprotected (removal of the tert-butoxycarbonyl group), as described previously, to give (4E)-N-methyl-5-[3-(5-trans-beta-styrylpyridin)yl]-4-penten-2-amine. Similar second coupling with ethynylbenzene, and subsequent deprotection, will give (4E)-N-methyl-5-[3-(5-phenylethynylpyridin)yl]-4-penten-2-amine.

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