ChemInform Abstract: 1,3‐Oxazin‐6‐ones: Versatile Intermediates in Heterocyclic Synthesis

Heterocyclic β‐Enamino Esters, 48 1) Heterocondensed Pyridines by Cycloaddition‐Extrusion Sequence of Bi‐ and Tricyclic 1,3‐Oxazinones with N,N ‐Diethyl‐1‐propynylamine

“…The synthesis of the heterocyclic and heteroaromatic p-enamino esters 5a, 7a, 9a, and l l a is described in C19H28N2S (316.5) Calcd. C 72.10 H 8.92 N 8.85 Found C 72.01 H 8.96 N 8.63 4- (Diethylamino) -5,6,7,8-tetrahydro-3-methyl-2-phenylbenzo- [4,5]thieno [2,3-b] -12,19), 19.19 (C-10,17), 46.35 (C-l1,18), 120.63 (C-4a,4b), 122.93 152.94 (C-4,5), 158.21 (C-8a,9a), 159.22 (C-2,7). -MS: m/z = 508 1.00 (t, 12,19-H, J = 7 Hz), 2.35 (s, lO,l7-H), 3.34 (q, ll,lS-H, J = (C-3,6), 128.18 (C-15,16,22,23), 129.96 (C-14,21), 141.06 (C-13,20), C 75.76 H 7.13 N 11.02 Found C 75.85 H 7.10 N 11.02 5-(Diethylamino)-N.N-diethyl-3,4-dihydro-3,6-dimethyl-4-0~0- 2,7-diphenylthieno(2.3-b : 2.53 (dq,J = 12.6;7 Hz),3.30 (dq,J = 12.6;7 Hz),3.42 (m, (m, H,,), Har.).…”

1,2,4‐Triazine vs. 1,3‐ and 1,4‐Oxazinones in Normal‐ and Inverse‐Electron‐Demand Hetero‐Diels–Alder Reactions: Establishing a Status Quo by Computational Analysis

“…For decades 1,2,4-triazine (1), [1][2][3][4][5][6][7][8][9][10] 1,3-oxazin-6-one (2), [11][12][13][14] 1,4-oxazin-2-one (3), [15,16] pyrazines 4 [1][2][3]15,17] and pyrimidines 5 [1][2][3] (Scheme 1) have been utilized as 2-azadienes in inter-and intramolecular hetero-Diels-Alder (DA) reactions with alkynes, alkyne equivalents (i.e., substituted alkenes with leaving groups amenable to elimination) and heterocycles (i.e., indoles), to prepare functionalized pyridines 6 via bicyclo[2.2.2] intermediates 7. Un-functionalised alkenes have also been investigated with these systems (i.e., 1-5), giving rise to heterobicyclo[2.2.2] compounds 9, which can undergo further transformations, but these are generally not associated with pyridine formation.…”

“…Un-functionalised alkenes have also been investigated with these systems (i.e., 1-5), giving rise to heterobicyclo[2.2.2] compounds 9, which can undergo further transformations, but these are generally not associated with pyridine formation. [1][2][3]12,[16][17][18] By considering the 2-azadiene heterocyclic systems available (1-5) direct comparisons of relative reactivities and selectivities are, however, difficult to ascertain from the literature. Steglich [12] has suggested that a lower degree of reactivity and regioselectivity can be expected for 1,4-oxazin-2-ones 3 as compared to 1,3-oxazin-6-ones 2, and Boger [21] suggests the reactivity of similar substituted 1,3-oxazin-6-ones 2 is comparable to 1,2,4-triazines 1.…”

“…[1][2][3]12,[16][17][18] By considering the 2-azadiene heterocyclic systems available (1-5) direct comparisons of relative reactivities and selectivities are, however, difficult to ascertain from the literature. Steglich [12] has suggested that a lower degree of reactivity and regioselectivity can be expected for 1,4-oxazin-2-ones 3 as compared to 1,3-oxazin-6-ones 2, and Boger [21] suggests the reactivity of similar substituted 1,3-oxazin-6-ones 2 is comparable to 1,2,4-triazines 1. A further example that adds confusion to the situation is that 1,3-oxazin-6-ones 2 react with both electron-poor [19] and -rich [20,21] acetylenes to afford pyridines, depending on the substitu-in the unsubstituted cases 1,2,4-triazine is less reactive in comparison to 1,3-oxazin-6-one and 1,4-oxazin-2-one for both reaction modes, whereas the cycloaddition regioselectivities depend largely on the diene.…”

Structure of a 7-oxa-2,8-diazatricyclo[3.2.2.02,4]non-8-en-6-one intermediate in a 4H-1,3-diazepine synthesis

“…The synthesis and chemistry of compound (3) is given in a paper by Steglich, Jeschke & Buschmann (1986). No crystal structure with a similar tricyclic skeleton could be found in the literature.…”