Current Organic Synthesis - Volume 12, Issue 4, 2015

One of the actual goals in the field of macrocyclic research is to provide accessible chemically robust compounds with absorption in the NIR spectral region. This requirement can be fulfilled in the case of tetrapyrrolic derivatives such as porphyrins, phthalocyanines etc with extended system of electronic conjugation. In this short review, we focus on the available approaches for the synthesis of cycl[3.2.2]azine-1,2-dicarboxylic acid functional derivatives – an emerging class of π-extended tetrapyrrolic macrocycle precursors.

To generate series of useful compounds from hydrocarbons, various reactions which are able to satisfy these requests such as addition reactions to carbon/carbon multiple bonds, nucleophilic ring-opening reactions, carbonyl chemistry of the “non-aldol” type, cycloaddition reactions and so on have been studied in-depth. And in general, the preactivation of coupling synthons is always required for such cross-coupling methodologies. However, some existing downsides such as complicated processes and low efficiencies have kept the costs of the classical cross-coupling reactions very high. Due to its advantages such as higher yields of the desired product, relatively fewer byproducts and higher functional-group tolerance over the classical cross-coupling reactions, direct C-H functionalization is thought to be one of the most atom-economical synthetic processes. To develop better, faster, cheaper ways for converting the highly abundant hydrocarbons to value-added chemicals, carbon–hydrogen (C–H) activation is becoming one of the most powerful synthetic tools. As time goes on, C-H activation will find its wider application in a variety of catalytic processes in the pharmaceutical industry, materials science and other industries.

This review primarily focuses on the publications within the last 25 years (i.e. from 1990 to 2014) related to the advances in the synthesis and reactions of annulated 3-amino-4-iminopyrimidines. The literature results covered in this review demonstrate that the studied reactions are chemo-selective.

The bisabolane sesquiterpenes, which have been isolated from different natural sources, are an important class of compounds. They exhibit a wide range of biological activities. They have a benzylic stereogenic centre, carrying a methyl group at this position. Among the major group of bisabolane sesquiterpenoids, curcumene is an aromatic compound, which has been widely studied. (S)-(+)-curcumene is a constituent of the essential oil from the rhizomes of Curcuma aromatica and is an odour component of distantly related corals. A new application of curcumene has been described as insecticide, repellent, and insect feeding deterrent. For this reason, the synthesis of this compound has been the subject of considerable interest during the past 15 years and several syntheses of the enantioenriched (R)-(-)-curcumene have been reported. In this review, we focus the attention on the recent syntheses and applications of this natural compound.

The development of smart supramolecular gelators whose self-assembly propensity can be controlled by physical processes such as sonication is highly interesting. Upon sonication, the designer gelators form in situ gel in organic solvents or water with diverse folding and assembly. These sonication responsive supramolecular gels have various applications such as switches, extra cellular matrix for tissue engineering, advance materials, drug delivery vehicles and controlled release systems. This contribution will review the latest advancements in the synthesis of gelators that are responsive to ultrasound.

Reported here are two novel cationic domino reactions of 2-arylmethylideneindoxyls leading to the formation of highly substituted dispiropseudoindoxyls or 9-oxo-pyrrolo[1,2-α]indoles. The outcome of the reactions can be controlled by the appropriate choice of an acid or the application of an external nucleophile. The dispirocyclodimers are formed in single diastereomeric forms with three stereogenic centers, with two of those being quaternary. The reactions provide approaches to the spiropseudoindoxyl and pyrrolo[1,2-α]indole ring systems, common components in natural spiropseudoindoxyl alkaloids and pyrrolo[1,2-α]indole biologically active molecules.

Superparamagnetic nanoparticle-supported imidazole (Im@MNPs) was prepared and used as magnetically separable catalyst for Knoevenagel condensation of aromatic aldehydes with active methylene compounds. 3.0 mol% of Im@MNPs with water as solvent was investigated as the optimal catalytic system. The active methylene compounds involved malononitrile, ethyl 2-cyanoacetate, 2-(1H-benzo[d]imidazol-2-yl)acetonitrile, 2- (benzo[d]thiazol-2-yl)acetonitrile, 2-phenylacetonitrile, 2-(3-chlorophenyl)acetonitrile, 2-(1H-indol-3- yl)acetonitrile. All reactions preceded smoothly affording target products in good to excellent yields (78-99%) within minutes to hours. More importantly, the catalyst could be reused up to ten times with only a slight decrease in catalytic activity. A plausible mechanism was proposed to rationalize the high catalytic activity of catalyst.

Starting from 4-ethylguajacol in only 3–4 steps the new photolabile protecting group (PPG) precursors AMNPPol and AMNPPOCOCl can be obtained, which are suitable for the protection of the N- and the C-terminus of amino acids and peptides. The incorporated allyl functionality allows subsequent ring closing reactions with other unsaturations in the peptide. These protecting groups can be removed faster than the commonly used (substituted) nitrobenzyl protecting groups.

Diversity oriented, efficient and environmentally benign synthetic protocol has been presented for the synthesis of spiroquinazolinones. The hybrid drug-like small molecules incorporating medicinally privileged heterocyclic systems have been synthesized by tandem reaction of 3-aminocrotonnitrile, phenyl hydrazine/ hydrazine hydrate, isatoic anhydride and isatin using deep eutectic solvent as efficient catalyst and environmentally benign reaction medium.