Spiroheterocyclics

The purpose of this study was to explore the introduction of an OZT moiety onto the specific C-3 site of both l,2 5,6-di-0-isopropylidene-a-D-glucofuranose and 1,2 4,5-di-0-isopropylidene-p-D-fructopyranose, taking advantage of the well-defined frame of both carbohydrate structures to generate all possible OZT-isomers. These spiroheterocyclic structures could be constructed according to a simplified sequence based on a key stereoselective approach from uloses via epoxides or aziridines (Scheme 16). 

One of the first mentions about reaction products with angular structure was published by Desenko and co-authors in [94]. It was shown that multicomponent treatment of 3-amino-l,2,4-triazole with two equivalents of cyclohexanone yielded spiroheterocycles 61 (Scheme 29). 

Water-based green protocol under conventional heating was used in another publication [112] to carry out three-component treatment between 3-substimted 5-aminopyrazoles, barbituric acids, and several isatines. The reaction gave up required spiroheterocycles 77 in excellent yields and purity (Scheme 33). 

When the 1,3-dicarbonyl substrate reacts twice via its activated methylene due to the presence of heteroatoms blocking the enolization process on other positions, spiranic systems are formed in the presence of two equivalents of aldehyde and an equivalent of urea (Scheme 15) [85]. The reaction can be promoted either in acetic acid as solvent or neat under microwave irradiations or in the presence of H3PW12O40 as catalyst. Finally, this technique for generating spiroheterocyclic products has been transferred to solid-supported methodology by immobilizing the 1,3-dicarbonyl partner onto a resin [86]. 

Scheme 15 Three-component synthesis of spiroheterocyclic Biginelli s products...

Habib-Zahmani H, Viala J, Hacini S, Rodriguez J (2007) Synthesis of functionalized spiroheterocycles by sequential multicomponent reaction/metal-catalyzed carbocylizations from simple beta-ketoesters and amides. Synlett 1037-1042... 

The D-<2/ <2 z o-hex-2-ulopyranosonates have been used as building blocks for the synthesis of spiroheterocyclic carbohydrates.276,277 The glycosyl donor, methyl (3,4,5-tri-O-acetyl-/J-D- rafo 0-hex-2-ulopyranosyl)onate bromide (102), obtained from the methyl ester of D-uraftinn-2-hexulosonic acid may be converted into its nitrophenyl a-glycoside, which in turn is reductively cyclized to the spirane 103 (Scheme 8). 

Fundamentally, optical isomers of the spiroheterocyclic cobalt complex must exist. Since these compounds could not be separated, we tried to synthesize the dicyano derivative under CO substitution by reaction with KCN in liquid NH3 in the hope that a separation into the optical antipodes might be possible. At 120°C, however, the reaction gave, besides K2[Co(NO)(CO)(CN)2], a complex in which the C(CH2PPh2)4 ligand is tridentate (139) ... 

Substitution of two carbons in position 2,3 of the pentadienyl anion (see Section 6.1) creates a type 2,3 system. Such molecules are the dihydropyrazolo-pyridines (DHPP) 42.50 51 The 1,3 dipolar cycloaddition reaction, which is so effective as a method for synthesizing five-membered rings, can also be used to prepare spiroheterocyclic compounds of the 2,3 type. If a suitable bromo-substituted dibenzopentafulvene is reacted with pyridine the pyrazolo-pyridine 42 is formed in 30-90% yields (Scheme 18). 

Alkylidene imidazoles are best described as either ketene acetals or enamines, depending on the positions of substitution. 2-(2-Propylidene)imidazoles such as 787 (Scheme 195) react with azides to form spiroheterocycles 788. The reaction rates vary widely depending on the hybridization of C(4)-C(5) bond of the dipolarophiles dihydroimidazoles react in days while imidazoles take only hours <2005HCA1589>. 

For the determination of Ke of different spiroheterocycles (11-20, 42-47), Hellrung and Balli22 chose for eMC the molar absorptivity of the corresponding protonated form, thus causing a considerable error in the Ke values obtained. 

Photo-, thermo-, solvato-, and electrochromic spiroheterocyclic compounds 04CRV2751. 

A mixture of Meldrum s acid or barbituric acid derivatives, urea and aldehyde gave 99, stereoselectively. Reaction of 2-methylene indoline derivatives with l-nitroso-2-naphthol gave 100. Spiroheterocycles 101 were prepared from a mixture of isatin and aromatic or heterocyclic... 

Similarly, secondary cnaminoncs substituted in the jU-position by a quinonylmethyl group easily cyclize to spiroheterocycles, demonstrating the nucleophilic potential of enaminone nitrogen. The corresponding primary quinonylmethylenaminones are suitable starting materials for the synthesis of 6-hydroxyquinolines (equation 97). 

Spiroheterocycles (187) of alternating C=0 and NR building units were constructed by the... 

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