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Issue 8, 2000
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Substituted 3,4-pyridynes: clean cycloadditions

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The stabilisation of 3,4-pyridyne (1) by an alkoxy group adjacent to the ring nitrogen is reported. The regioselective lithiation of 2-ethoxy- (14), 2-methoxy- (18), 2-isopropoxy- (19) and 6-isopropoxy- (26) -3-chloropyridines with tert-butyllithium at low temperatures, followed by elimination of lithium chloride affords 2- and 6-alkoxy-3,4-pyridynes. These species are trapped in situ with furan in a Diels–Alder reaction to give 5–8 in 66–89% yield, and do not give products typical of polymerisation or nucleophilic addition to the 3,4-pyridyne intermediates. As a comparison treatment of 3-chloropyridine with furan and LDA gives only 19% of adduct (4). We also report the novel use of the isopropoxy (rather than methoxy) group in these systems, which can act as a heteroatomic electron donating group which inhibits α-lithiation by tert-butyllithium because of its increased steric bulk.

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Publication details

The article was received on 13 Dec 1999, accepted on 28 Feb 2000 and first published on 31 Mar 2000

Article type: Paper
DOI: 10.1039/A909772D
Citation: J. Chem. Soc., Perkin Trans. 1, 2000,0, 1245-1249
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    Substituted 3,4-pyridynes: clean cycloadditions

    S. J. Connon and A. F. Hegarty, J. Chem. Soc., Perkin Trans. 1, 2000, 0, 1245
    DOI: 10.1039/A909772D

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