Methyl 5´-acetyl-2´-amino-6´-metil-2-oxospiro[indoline-3,4´-4H-pyran]3´-carboxylate

Abstract

Spiro-cyclic derivatives of 2-oxindole are interesting objects for searching of new physiologically active substances (Cingolant et al., 1989, Urbahns et al., 2000). However, such compounds containing the 2-amino-4H-pyrane fragment have not been investigated. In this paper we report the molecular and crystal structure of the spiro[indolin-3,4-(5-acetyl-2-amino-3carbethoxy-6- methyl-4H-pyran)]-2-one (Fig. 1) which can be considered as a potential melatonin analogue with a rigid etanamide side chain. Dihydroindolone fragment is planar within 0.01 Å and spiro-joined to the dihydropyrane ring; esterified carboxyl group and the C18, N2, and C16 atoms are co-planar within 0.03 Å and are turned with respect to the bicyclic fragment for 116.2 (2) ° (the C1—C6—C7—C9 torsion angle). The formation of hydrogen bond promotes the elongation of the C11—C12 and C13—O3 bonds (Table 1) in comparison with their mean values (Bürgi & Dunitz, 1994) 1.320 Å and 1.210 Å, respectively and the shortening of the C11—N2 and C12—C13 bonds (the mean value are 1.336 Å and 1.455 Å, respectively). The repulsion between substituents at the C9—C10 double bond (the shortened intramolecular contacts H17c···C10 2.81 Å, H17c···C18 2.76 Å, H18b···C16 2.63 Å, H18c···C17 2.64 Å [the sum of van der Waals radii is 2.87 Å (Zefirov & Zorky, 1995)], C18···C17 3.19 Å (3.42 Å) leads to an increase of the C9—C10—C18 bond angle up to 128.6 (2) °. The formation of the N2—H2Na···O3 intramolecular hydrogen bond (Table 2) supports the coplanarity of the carboxyl group and dihydropyrane ring. In the crystal molecules of (I) are connected by the intermolecular hydrogen bonds N1—H1N···O1' and N2—H2Nb···O1' (Table 2, Fig. 2).