Flash vacuum pyrolysis of N-allyl-substituted 1,3,4-oxadiazolin-5-ones

Synthesis of Novel Tetrahydro-1<i>H</i>-pyrazolo[4,3-<i>c</i>]pyridines <i>via</i> Intramolecular Nitrilimine Cycloaddition

“…Intramolecular 1,3-dipolar cycloaddition of nitrilimines with alkynes is a well documented method for the preparation of fused polycyclic pyrazoles. 10,11) While nitrilimines have been obtained by a number of means including the thermolysis of 2,5-disubstituted tetrazoles 12) or 1,3,4-oxadiazolin-5-ones, 13) the photolysis of sydnones, 14) and the oxidation of aldehyde hydrazones, 15) they are most conveniently derived from the reaction of hydrazonoyl chlorides with base or silver salts. 16) This approach required the preparation of acyl hydrazide 16 as illustrated in Chart 3.…”

Pteridines. 48. Utilization of 3,3-dimethoxy-2-pyrrolidinopropene for the synthesis of folic acid, N2'-acetyl-7-folic acid, and 5-deaza-7-folic acid

“…3,3-Dimethoxy-2-pyrrolidinopropene (7). A mixture of 23.6 g (0.2 mol) of pyruvaldehyde dimethyl acetal, 28.4 g (0.4 mol) of pyrrolidine, 6 g of anhydrous magnesium sulfate, and 90 mL of anhydrous ethyl ether was stirred mechanically at room temperature.…”

“…The product was filtered off and washed successively with cold methanol, water, methanol, and finally ether to leave 2.68 g (71%) of a yellow powder, mp 208-209.5 °C. The analytical sample was prepared by recrystallization from methanol with no change in melting point: NMR (Me^O-dg) 3.40 (s, 6 H, (OCH3)2), 5.23 (s, 1 H, CH), 6.60 (br s, 2 H, NH2), 7.65 (br s, 2 H, NH2), 8.33 (s, 1 H, C-6 H); IR (KBr) 3320, 3110, 1625 cm"1.…”

“…The mother liquors were concentrated in vacuo and the residue was triturated with ether to give a dark red powder which was collected and recrystallized from methanol to give an additional 2.9 g (80% total yield) of dark yellow crystals, mp 156-158 °C. The analytical sample was prepared by recrystallization from methanol: mp 157-159 °C; NMR (CDCI3) 1.85-2.10 (m, 4 H, CH2CH2), 3.42 (s, 6 H, (OCH3)2), 3.52-3.94 (m, 4 H, N(CH2)2), 5.13 (s, 1 H, CH), 5.45 (d, <7 = 13.5 Hz, 1 H, C-3 H), 7.75 (d, =7 = 13.5 Hz, 1 H, C-2 H); IR (KBr) 2202,2195,1565,1443 cm"1.…”

“…The mixture was then heated to reflux for 24 h under nitrogen, filtered hot, allowed to cool to room temperature, and then refrigerated to give 3.08 g (65%) of fine white needles, mp 223-224 °C. Recrystallization from 1-butanol provided the analytical sample without any change in the melting point: NMR (Me^O-de) 3.33 (s, 6 H, (OCH3)2), 5.18 (s, 1 H, CH), 6.25 (br s, 2 , NH2), 7.10 (d, «7 = 8 Hz, 1 H, C-6 ), 7.50 (br s, 2 H, NH2), 8.42 (d, <7 = 8 Hz, 1 H, C-5 H); IR (KBr) 3380, 3320, 3150, 1632,1602 cm"1.…”