Oxo heterocyclic

Another tetracyclic carbon skeleton, named cumbiane, has been isolated from Pseudopterogorgia elisahethae. Its representatives are the diterpenoids cumbiasin A (33) and B (34) [20] their structures and relative configurations were elucidated by interpretation of a combination of spectral data. The six-membered ring D was formed by connecting CIO and C16 of an elisabethane carbon skeleton. The carbocyclic skeleton of the cumbiasins is unprecedented and represents a new class of C20 rearranged diterpenes. The tricyclic seco-cumbiane skeleton is derived from the cumbiasins by cleavage of the C15-C16 bond. Due to intramolecular cyclizations two additional oxo-heterocycles are present in cumbiasin C (35) [20] (Fig. 7). 

The enantioselective hetero-Diels-Alder (HDA) reaction of carbonyl compounds with 1,3-dienes represents an elegant access to optically active six-membered oxo-heterocycles. Since the pioneering work of Rawal et al. in 2003 [55], the enantioselective HDA reaction catalyzed by diols (such as TADDOLs) has become a flourishing field of research [56]. 

Anodic oxidation of JV,N-dimethyl-co-hydroxyamides (57) in CH3OH-Bu4NBF4 at a platinum anode leads to formation of N-methoxy-JV-methyl-co-hydroxyamides (58) in high yield.116 The latter could in some cases (formation of five-, six-, and seven-membered rings) easily be transformed to l,3-oxaza-4-oxo heterocyclic systems (59) by acid catalysis [Eq. (49)]. No direct formation of the 1,3-oxazaheterocycles was observed, e.g., 57++59. An intramolecular addition of the hydroxy group to the intermediate acylam-monium ion is believed to be hindered by adsorption phenomena at the anode surface. 

N-heterocyclics, hydroxy, N-condensed imines, cyclic N-macrocyclics oxo-heterocyclics silyl-N-heterocyclics... 

Conjugate addition of p-oxo heterocyclic sulfones afforded intermediate oxosulfones. Inspired by the Julia-Kocienski methodology, a Smiles rearrangement performed in a one-pot operation afforded corresponding all nyl or alkenyl derivatives (Scheme 8.11). ... 

The equilibrium position for the three tautomers (C-H tautomer 5, N-H tautomer 6, and 0-H tautomer 7) is dependent on the pyrazolone substituents and the solvent used. Tautomerism with substituent participation is observed in oxo heterocycles as well as for the corresponding thiones and imines. 

Azetidines, four-membered cyclic imines and their derivatives were also investigated regarding their cationic polymerization in the early 1980s. In analogy to the polymerization of aziridine, hyperbranched structures are obtained by the same mechanism as described previously. Still, the difficult monomer preparation and the limitation of molecular weights due to rather low reactivity of the chain end compared to oxo-heterocycles limited the interest in these polymers. By using the derivative N-phenylazetidine (Scheme 3), the formation of linear chains can be favored. Branching termination reactions are suppressed because of the decreased... 

Danishefsky s diene (85) and aldehyde to give the corresponding optically active six-membered oxo heterocycles (86) in up to 98% ee. The absolute configuration (R) of the product was controlled by (87), although the results were dramatically improved, particularly with regard to reactivity, in the presence of diamines and were also independent of the stereochemistry (R or S) of the diamines. 

The nucleophilic substitution reactions in pyrido-[2,3-f>]- and -[3,4-f ]-pyridazines in general follow the usual pattern of polyaza heterocycles. Oxo groups in the 2-, 3- and 6-positions of [2,3-f ]-ones, and in the 2- and 3-positions of [3,4-f ]-ones have been... 

Heterocyclic compounds carrying potential hydroxyl groups are cyclic amides or vinylogs of amides. There is much physical evidence that acyclic amides exist almost entirely in the oxo form (for references see reference 6), and the apparent contradiction that ultraviolet spectral data appeared to favor the imidol formulation has now been explained on steric grounds. The value of pKr is estimated to be about 7 on the basis of pK measurements for acyclic amides. Extensive evidence, summarized in the following sections, shows that for a- and y-hydroxy heterocyclic compounds, the cyclic amide form usually predominates by a substantial factor, often ca. 10 . 

The oxoaporphine alkaloids Teliglazine (126), Corunnine (127), Nandazurine (128), PO-3 (129), A-Methylliriodendronine (130), and A,(9-Dimethylliriodendronine (131) contain the 6-methyl-7-oxo-dibenzo [Je,g]quinolinium-l-olate ring system 125 which is isoconjugate with the l-methyl-7-methylene-7H-benzo[Je]anthracene anion (Scheme 46). Therefore, these alkaloids belong to class 1, i.e., heterocyclic mesomeric betaines isoconjugate with odd alternant hydrocarbon anions. Another... 

Heterocyclic compounds carrying hydroxyl groups may be compared with phenols. Thomson has reviewed the tautomeric behavior of phenols often both tautomeric forms of polycyclic compounds such as naphthols can be isolated. Early work on hydroxy-thiophenes and -furans was also reviewed by Thomsond but until recently their chemistry has been in a somewhat confused state. A pattern is now beginning to emerge, at least for the a-substituted compounds, which appear to exist as A -oxo derivatives and to attain equilibrium slowly with the corresponding A -oxo forms. For the a-hydroxy compounds, the equilibrium generally favors the A -oxo form. 

All the available evidence suggests that five-membered heterocyclic compounds containing a potential hydroxyl group between the two hetero atoms in the 1- and 3-positions exist predominantly in the oxo form (cf. 89 90). 

Reaction of 2-oxo-2,3-dihydropyrido[l,2,3- /e]-l,4-benzoxazinium chloride (253) with 1 and 2 mol of the appropriate heterocyclic quaternary salt 254 in the presence of a few drops of piperidine gave mono and bis condensation products 255 and 256, respectively (98MI45). Similar reactions of 2-arylpyrido[l,2,3- /e]-l,4-benzoxazinium bromides and 254 [R = R =-(CH=CH)2-] yielded condensation products 257 (X = 0). 

Bromo atom of ethyl (3S)-10-bromo-3-methyl-7-oxo-2,3-dihydro-7//-pyrido[l,2,3- fe]-l,4-benzothiazine-6-carboxylate was change for hetaryl groups with tributylstannyl derivatives of heterocycles in the presence of (Ph3P)2Pd(II)Cl2 in boiling toluene (OOMIPIO). 7-Aryl-5-oxo-2,3-dihydro-5//-pyrido[l,2,3- fe]-l,4-benzothiazine-6-carboxylates, 6-carboxamides and their 1,1-dioxide derivatives were prepared from 7-chloro derivatives in the... 

Heterocyclization of chlorosulfonyl isocyanate with ethyl-3-oxo-2-(arylhydrazono)butanoates 1011 (2 1) gave thiadiazolotriazinediones 1012 (91H1517) (Scheme 188). 

As noted previously, a wide variety of aromatic systems serve as nuclei for arylacetic acid antiinflammatory agents. It is thus to be expected that fused heterocycles can also serve the same function. Synthesis of one such agent (64) begins with condensation of indole-3-ethanol (60) with ethyl 3-oxo-caproate (61) in the presence of tosic acid, leading directly to the pyranoindole 63. The reaction may be rationalized by assuming formation of hemiketal 62, as the first step. Cyclization of the carbonium ion... 

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