Nitrogen bridgehead compounds. Part X (1). ¹H and ¹³C nmr study of pyrido[1,2‐a]pyrimidines

Abstract

By 1H nmr, the predominance of the conformer with a quasi‐axial 6‐methyl group was established for the pyrido[1,2‐a]pyrimidines I‐III. The 13C nmr spectra of I‐III were completely assigned. The conjugative effect of substitution at G‐3 on 1H and 13C chemical shifts of the C‐9 methylene group parallels its effect on reactivity.

Stereochemical studies. Part 92. Nitrogen bridgehead compounds. Part 61. Synthesis and X-ray analysis of 4,8-dimethylperhydrocyclopenta[d]pyrido[1,2-a]pyrimidin-10-one diastereoisomers

“…If we disregard the phenolic oxygen atoms, the picrate molecules are related by a pseudo-centre of symmetry. A very similar arrangement was found in a hexahydropyrid0 [2,14]quinazolinium picrate. This pseudo-symmetry might have caused the difficulties in the application of direct methods.…”

Nitrogen bridgehead compounds. Part 29. Tautomerism and Z–E isomerism of ethyl 9-aminomethylene-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylates and their homologues

“…data are shown in Table 2. In the spectra of (2)- (6) only one set of signals can be observed whilst (7) shows a doubling of several resonance lines in its spectra with an intensity ratio of 88 : 12. The doubled signals may be assigned to E-and 2-isomers, respectively, so the coexistence of this isomer serves as a proof that the rate of 2-E interconversion must be slow on the n.m.r.…”

“…Institute of Organic Chemistry Technology, Technical University, Budapest H-752 1 , Hungary H and 3C n.m.r. studies have proved that ethyl 9-dimethylaminomethylene-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[lI2-a] pyrimidine-3-carboxylates (2)- (5) and the corresponding pyrrolo homologue (6) exist in the form of €-isomers whereas the azepino[Il2-a]pyrimidine derivative (7) appears as an equilibrium mixture of Z-and €-isomers. On the basis of l5N chemical shifts an analogous tautomeric structure has been established for the 9-dimethylaminomethylene derivatives (2)- (7) and the ethyl 9-arylaminomethylene-4-oxo-6,7,8,9-tetra hydro-4H-pyrido [ 1,2-a] pyrimidine-3-carboxylates (8)-( 1 2) as well.…”

Alkaloids from Delphinium geyeri. Three new C20-diterpenoid alkaloids

“…Geyerine (1) was isolated as a pure (TLC, 360-MHz NMR) glassy amorphous solid which turned translucent on standing but could not be crystallized: Silica gel TLC Rf 0.32 (10:1 CHClg/ MeOH) and 0.67 (30:5:1 EtOAc/EtOH/NH4OH); [ ]2^+ 9.6°( c 0.36, EtOH); HREIMS, m/z (relative intensity, formula) 427.2341 (16, C2gH33N05), 410.2331 (5, C22H32N04), 342.1701(10, C20H24NO4), 327.1781(22, 12C1913CH24N03), 326.1746, 325.1665 (20, C^H^NOg), 298.1801 (25, C19H24N02), 269.1774 (7, C^NO); IR (thin film, cm"1) 3360, 2930,1725,1705, 755; 13C NMR (CDClg, 90.5 MHz) Table II; UV Xmax (EtOH) 252 sh, 297 sh; NMR (CDClg, 360 MHz) 5.14 (ddd, J = 1 Hz, J = 91 (22), 74 (46), 57 (100); UV XmM (EtOH) 230 sh, 257 sh, 285 sh; IR (CH2C12, cm"1;3595, 2910,1727,1360,1225,1065,1040 NMR (360 MHz, CDClg) 5.13 (dd, «7 = 9 Hz, J = 3 Hz, J = 1 Hz, C-11H), 4.94 (br s, C-17Ha), 4.86 (d, J = 4 Hz, C-3H), 4.78 (br s, C-17Hb), 4.32 (slightly broadened d, J = 9 Hz, «7=1 Hz, «7 < 1 Hz, C-13H), 4.13 (m, W1/2 = 12 Hz, C-2H/3), 3.76 (s, C-20H), 3.48 (d, =7 = 12 Hz, C-19Ha), 3.12 (dd, «7 = 15 Hz, J = 2 Hz, C-), 3.02 (d, =7 = 12 Hz, C = 19 Hb), 2.64 (m, 1 ), 2.50-2.20 (m, 4 ), 2.15 (s, 3 ), 2.10-1.82 (m, 6 ), 1.73 (m, 1 ), 1.60-1.48 (m, 2 ), 1.40 (s, 3 H, C-18), 1.32 (s, 1 ), 1.21 (d, J = 7 Hz, 3 ), 0.95 ppm (t, 3 H); 13C NMR (25 MHz, CDClg) Table II.…”

“…The downfield portion of the XH NMR spectrum showed one proton resonances at 4.86 (CHOAc, d, J = 4 Hz) and 4.13 ppm (CHOH, br s) which were shown to be on adjacent carbons by a decoupling experiment. The 4.13-ppm resonance was further coupled to resonances appearing at 3.12 and 2.05 ppm (2 and 4 Hz, respectively). The latter two were themselves coupled {J = 15 Hz).…”