Synthetic routes to thiazoloindoles

Several structural types of thiazoloindoles can be distinguished with regard to the position of the fusion between the thiazole, benzene, and pyrrole rings. The present review describes the synthetic routes to five selected types of thiazoloindole derivatives with [3,2-a], [3,4-a], [5,4-b], [5,4-e], and [4,5-e] fusion. These compounds are useful for the discovering of future targets and the development of new drug molecules.     

Synthetic routes to imidazothiazines

This review article presents the available synthetic routes for the preparation of different types of imidazothiazines. Imidazothiazines dealt with are classified into five types based on the position of linkage between imidazole and thiazine rings. The importance of the latter compounds in pharmacology is also discussed. The main purpose of this review is to present a survey of literature on imidazothiazines and provide useful and up-to-date data to organic and medicinal chemist, since such compounds have not been reviewed before.     

Synthetic routes to 5,10,15-triaryl-tetrabenzocorroles

Two different synthetic routes for the preparation of 5,10,15-triaryl-tetrabenzocorroles have been developed. The first approach is based on the condensation of a tetrahydroisoindole with aryl-aldehydes, and the second pathway involves a cross-coupling reaction between a bromo-substituted corrole and a suitable substrate to form the four β-fused aryl rings. These routes are successful to lead to the target tetrabenzocorroles, obtained in both cases as the corresponding Cu complex and with the highest yield obtained via the one-step cross-coupling methodology. Demetalation of the Cu-tetrabenzocorrole produces the corresponding free base; this macrocycle was further exploited to obtain the Sn and Co complexes in good yields.     

Synthetic access to 5,10-disubstituted porphyrins

A simple acid-catalyzed condensation of unsubstituted tripyrranes with pyrrole and various aldehydes affords 5,10-disubstituted-β-unsubstituted porphyrins by the ‘3+1’ approach in low to moderate yields. A complementary synthesis of similar compounds involves reaction of unsubstituted porphyrin (porphine) with organolithium reagents in good yields.     

Heterocyclic steroids: Synthetic routes and biological characteristics of steroidal fused bicyclic pyrimidines

Natural steroids are characterized as a vital class of compounds, a type of secondary metabolites and components of cell membranes that widely accessible in plants or animals displayed significant pharmacological and varied biological properties. The present study aims to highlight the conveyed researches of synthetic routes adopted to obtain the various structures of steroidal fused bicyclic pyrimidines with substantial biological and pharmaceutical importance. The topic was discussed in light of the synthesis of fused [6 + 5] bicyclic systems, fused [6 + 6] bicyclic systems, binary heterocycles, and biological applications. In detail, the various synthetic strategies for the construction of steroids fused to bicyclic pyrazolopyrimidines, thiazolopyrimidines, triazolopyrimidines, pyridopyrimidines, pyranopyrimidines, and binary pyrimidines were discussed. Heterocyclic steroids of this class of compounds demonstrated potent anticancer, anti-proliferative, anti-neuro-inflammatory, anti-inflammatory, and anti-ulcer activities. It was perceived that the synthetic steroids of such bicyclic pyrimidine scaffolds are fused into the steroid basic skeleton is essential for the potent bioactivities.     

Synthetic routes for a new family of chiral tetradentate ligands containing pyridine rings

A series of new tetradentate ligands containing two bipyridine groups or two pyridine moieties carrying amine substituents has been synthesised either from 5'- and 6'-substituted chiral bipyridines, or from chiral pyridine derivatives. These precursors have been prepared from (-)-alpha-pinene or (-)-myrtenal, respectively. The structures of three tetradentate-, and of five chiral bipyridine ligands have been determined by X-ray diffraction.     

Synthetic routes to cyclopropylidenecarbinols and to cyclopropylidienes

Functionalized alkylidine cyclopropanes have beeen prepared from 1-seleno 1-vinyl cyclopropanes using [2,3] sigmatropic rearrangement of their corresponding selenonium ylides. A comparison with sulphur analogues is presented.     

Synthetic routes to indenopyridine analogues of morphactins

Investigation of a number of synthetic routes to aza analogues of Morphaetins led to the synthesis of (RS)-methyl 5H-5-hydroxyindeno[1,2-b]pyridine-5-carboxylate (6e) and the corresponding caboxamide. 6f.     

Synthetic routes to cristatic acid and derivatives

Synthetic paths to cristatic acid derivatives are explored and a convergent route to the total synthesis of these molecules is described.     

Synthesis of porphyrins bearing trans-thiols

[structure: see text] A route to porphyrins bearing trans-thiols is described using a thioacetyl-containing aldehyde or a thioacetyl-containing dipyrromethane in the presence of catalytic BF3 x OEt2 followed by oxidation. Metal complexation and ammonium hydroxide induced acetyl removal provides a route to these important molecular systems for future electronics experiments in which the thiols would serve as the adhesion points to gold probes.     

Neocuproine-KOtBu promoted intramolecular cross coupling to approach fused rings

Polycycles can be produced with different linkages (A, B = O, N, C, S) by constructing biaryl C-C bonds via neocuproine-KO(t)Bu promoted cross coupling between C-Xs and C-Hs.     

Synthetic routes toward carborane-wheeled nanocars

A new set of aryleneethynylene derivatives bearing three, four, and six p-carboranes as potential wheels attached to a semirigid chassis have been designed and synthesized. These molecules are expected to move in predetermined patterns on atomically smooth surfaces, depending on their specific configuration.     

Porphyrins with exocyclic rings. Part 21: Influence of pyrrolic and carbocyclic ring alkyl substituents on the synthesis of porphyrins bearing six-membered exocyclic rings

A series of 5-substituted 4,5,6,7-tetrahydroindoles were prepared by reacting 4-substituted cyclohexanones with phenylhydrazones derived from esters of acetoacetic acid under Knorr-type reaction conditions. Related 6,6-dimethyltetrahydroindoles were also prepared by reacting dimedone with oximes by the Knorr pyrrole syntheses, followed by selective reduction of the remaining ketone moiety with diborane. The substituted tetrahydroindoles were regioselectively oxidized with lead tetraacetate to give the related 7-acetoxy derivatives, and these reacted with 5-unsubstituted pyrrole esters to give pyrrolyltetrahydroindoles. In one case, a bromo substituent was used to protect the β-position of the pyrrole reactant. Cleavage of the benzyl ester protective groups with hydrogen over Pd/C, which also removes the bromo-protective group, gave four dipyrrole carboxylic acids. These were condensed with a dipyrrylmethane dialdehyde using the MacDonald ‘2+2’ condensation to give substituted porphyrins with six-membered exocyclic rings. These structures are useful for comparison to porphyrin samples found in organic-rich sediments such as oil shales and petroleum. The presence of methyl substituents on the six-membered ring for the tetrahydroindole precursors slightly decreases the yields for porphyrin synthesis, and this effect is enhanced when the system becomes more sterically crowded due to the presence of an ethyl group of the adjacent pyrrole ring. 5-Alkyl substituted tetrahydroindoles were also converted to tetrapropanoporphyrins via a cyclotetramerization procedure. The alkyl substituents again decreased the yields, although 5-alkyl substituents were found to have a far less deleterious effect than 6-alkyl groups. In addition to providing samples to help assign the vibrational spectra of geoporphyrin samples, these results demonstrate that highly substituted porphyrin systems can be prepared from tetrahydroindole derivatives.     

Heptaphyrins: Expanded porphyrins with seven heterocyclic rings

Expanded porphyrins containing seven pyrrole/heterocyclic rings linked in a cyclic fashion are termed heptaphyrins. The number ofπ-electrons in heptaphyrins depends on the number ofmeso carbon bridges used to link the heterocyclic rings, accordingly heptaphyrins with 28π-electrons and 30π-electrons are reported to date. Both condensation reactions of the appropriate precursors and acid-catalysed oxidative coupling reactions have been utilized to synthesise the heptaphyrins. The 30π heptaphyrins exhibit rich structural diversity where some of the heterocyclic rings in the macrocycle undergo a 180° ring flipping. An overview of the synthetic methods employed for the synthesis of heptaphyrins, their spectroscopic properties, structural behaviour and aromatic properties are highlighted in this paper. Dedicated to Professor C N R Rao on his 70th birthday