0-Enamino esters, heterocyclic

Enamines and imines, cyclic, 6, 147 Enamines as synthons in the synthesis of heterocycles, 72, 283 /j-Enamino esters, heterocyclic, as heterocyclic synthons, 38, 299 -Excessive heteroannulenes, medium-large and large, 23, 55... 

The syntheses of simple 1,3-oxazines (74AG596 86G361) from acylated amino acids (86G361) by treatment with dihalotriphenylphosphorane and of heterocondensed l,3-oxazin-4-ones from several N-acylated heterocyclic /3-enamino esters (81CB3188) have been implemented by aza-Wittig reactions of heterocyclic 2-(triphenylphosphoranylidenamino)esters with acid halides. 

The easily accessible aroylaminoimidazole-4-carboxylates (228) give imi-dazo[4,5-d][l,3]oxazin-7-ones (229) in a novel cyclization with dichlorotri-phenylphosphorane (Scheme 85) (93S107). Heterocyclic )3-enamino esters, such as 5-amino-2-(methylthio)thiazole-4-carboxylates and 4-amino-2-(methylthio)thiazole-5-carboxylates can also be used in both cases 1,3-oxazine rings are smoothly condensed to the existing heterocyclic ring (93S107). 

Wamhoff, H., Heterocyclic f-Enamino Esters, Versatile Synthons in Heterocyclic Synthesis, 38, 299. 

By addition of carbocyclic, acyclic and heterocyclic enamino ester to nitroalkenes and subsequent expulsion of the nitro group, pyrrole ester and fused derivatives are accessible82 (equation 58). 

Heterocyclic synthesis, see also Synthesis azodicarbonyl compounds and, 30, I heterocyclic -enamino esters and, 38,299... 

A broad choice of heterocondensed uracils are easily and generally accessible from heterocyclic /3-enamino esters and isocyanates (01LA200 03LA341). The mixed urea intermediate is smoothly cyclized with 5% aq. NaOH the whole procedure can be carried out in a one-step reaction, when pyridine serves as solvent and base catalyst for the ring closure (68CB3377 85AHC299) (Scheme 11). 

Heterocondensed uracils are easily accessible from acyllactones, -lactams, -thiollactones (72S151), and heterocyclic /3-enamino esters, especially (85AHC299). The latter gives a broad range of novel types of condensed systems. With the aid of the hexamethyldisilazane trimethyl-chlorosilane (HMDS/TMSC1) technique or the use of NaH and halo-sugars, respectively, simple approaches have been developed to obtain unusual nucleosides [92JPR(ip)] (Scheme 15). 

A. Heterocondensed Uracils from Lactones and Heterocyclic /3-Enamino Esters... 

Similarly, (heterocyclic) jS-enamino esters substituted with an electron donor as well as with an electron acceptor group ( push-pull ) show a decreased cycloaddition tendency towards 1,3-dipoles such as azides see (71c3B351o) and Section 4.11.4.7. 

Addition reactions. Heterocyclic J enamino esters of the dihydrofurarie type... 

Formation of a cation radical of the diene may catalyze Diels-Alder reactions with certain dienophiles thus oxidation of substituted vinylindoles to the cation radical in the presence of a push-pull dienophile may form different heterocyclic compounds by the Diels-Alder reaction, for instance pyrido[l,2i7]indoles from vinylindoles and yS-enamino-esters [33]. Similarly, anodic oxidation in MeCN of certain oxazolidines in presence of vinyl ether leads to derivatives of oxazepines in a catalytic reaction in which the ring-opened radical cation of the oxazolidine adds to the vinyl ether and the radical cation of the resulting oxazepine oxidizes the oxazolidine [34]. 

Heterocyclic -enamino esters as synthons for preparation of heteroeycies ... 

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