Where the Synthon Supplies Three Atoms

Of the two possibilities in this category (to supply N1+C2 + C3 or C2 + C3 + C4), only the latter has been employed, often by submission of a 3-pyridinamine to a Skraup-like synthesis. Typical examples follows. 

37%) 1047 and 1,5-naphthyridine 1-oxide (45) [O2NC6H4SO3H, H2S04, FeS04, 7H20, H3BO3, 0°C HOCH(CH2OH)2, substrate H20 then 130°C, 5 h 19%].1033 

6-Methyl-3-pyridinamine (50) with crotonaldehyde gave 2,6-dimethyl-1,5-naphthyridine (51) [substrate, 02NC6H4S03H, H2S04 ( ), H20, 125°C MeCH=CHCHO in slowly then 150°C, 8 h -10%] 1169 analogs somewhat similarly.269 

2-Bromo-6-ethoxy-3-pyridinamine (52) reacted with methyl 3-methoxyacrylate (2 equiv) to give 6-ethoxy-4-methoxy-l-(l-methoxy-2-methoxycarbony- 

---