During our synthetic study of monascorubrin (I),l which contains the extended pyrono-qulnonold system, there was found a simple method to make the new pyrono-qulnonold nucleus.
2 In this paper, a two-step synthesls of such a nucleus from a r-pyrone will be reported. Generally. the carbonyl group of a ppyrone has low activity toward the common ketone reagents. It was found, however, that a condensation reaction took place between 2,6-dlmethyl-V-pyrone and methyl cyanoacetate or malononltrlle In excess amounts of acetic anhydride to yield the extended kpyrone (II).3 Attempted acid hydrolysis of II under vigorous condltilorls gave only an amide (III) (m.p. 180 -181'C; m/e 223 (r+); )$3,r 3400, 3200. 1690, 1665. 1635. 1615, 1590 and 1520 cm-'), In which both amide and carbomethoxy groups resisted further hydrolysis. If we consider cyanoacetlc acid In excess acetic anhydrlde, the following equlllbrlum will be established. CN-CH2COOH + Ac20 = CN-CH2COOAc + AcCH Under such conditions, the mixed anhydrlde species could react with the ppyrone. Thus, 2,6-dlmethyl-r-pyrone4 in a large amount of acetic anhydrlde Me (II) R = CN (III) R.= CONH2 No.17
was reflaed with cyanoacetlc acid for on6 hour to give the condensation prouuct (IV) (m.p. 172 -173'C) in 30% yield. whose structure was supported