Current Organic Synthesis - Volume 9, Issue 4, 2012

The Editorial Board wishes to dedicate this issue of “Current Organic Synthesis” to the Editor-in-Chief of the journal, Prof. Dr. Atta-ur- Rahman, FRS, on his 70th birthday. The Editorial Board acknowledges the tremendous achievements of Prof. Rahman in the fields of Organic Chemistry in general and on bioactive natural products in particular. Prof. Rahman's honors include: the first scientist from the Muslim world to have won the prestigious UNESCO Science Prize (1999) in the 35 year old history of the Prize; elected as Fellow of Royal Society (London) in July 2006; conferred honorary doctorate degrees from many prestigious universities, including the University of Cambridge. On a national level his services are acknowledged in the form of four prestigious civil awards, including these highest national awards: Nishan-e-Imtiaz (2002), Hilal-e-Imtiaz (1998), Sitara-e-Imtiaz (1991) and Tamgha-e-Imtiaz (1983). At an academic level, Prof. Rahman has 856 publications in several fields of organic chemistry including 658 research publications, 21 patents, 113 books and 65 chapters in books published largely by major U.S. and European presses. He is currently the Editor-in-Chief of 12 scientific journals in fields ranging from Medicinal Chemistry to Pharmaceutical Drug Design. Seventy six students have completed their Ph.D. degrees under his supervision. He chairs the Network of Academies of Sciences of Islamic Countries (NASIC) and is the Vice-President (Central & South Asia) of the Academy of Sciences for the Developing World (TWAS) Council, and Foreign Fellow of Korean Academy of Sciences. Prof. Atta-ur-Rahman was the President of the Pakistan Academy of Sciences (2003-2006) and was again elected as the President of the Academy from 1st of January 2011. In particular, Prof. Rahman has made outstanding contribution to Current Organic Synthesis. The contributions of Prof. Rahman to the uplifting of science in Pakistan in his capacity as the Federal Minister for Science & Technology and later as Chairman Higher Education Commission were acknowledged by a high Civil Award of the government of Austria and TWAS prize for institution building as well as by four editorials in Nature. The Editorial board wishes health and prosperity to Prof. Atta-ur-Rahman in the years to come.

Without doubt, organic chemistry has made significant contributions in improving the qualities of our lives. However, there exists a demand for well-designed molecules of complex structures with additional requirements for low-cost and low-energy production of the materials, which stimulate us to consider innovative concepts in organic synthetic methods. In order to propose innovative methods for next-generation organic synthetic procedures, we present two strategies, (i) organic synthesis within two-dimensional molecular patterns and (ii) organic synthesis driven by molecular machines working at interfaces. For example, synthesis of stereo-regulated polymeric materials in two-dimensional molecular arrays, tip-induced chemical reactions at a solid surface, sequential reactions guided by polymer chains, DNA-nanorobots on two-dimensional DNA origami, ester hydrolysis based on modified behavior of protonated amines at an interface, and several other methods are introduced as pioneering and innovative concepts.

Modern organic synthesis requires easily obtainable chiral building blocks that show high chemical versatility for their application in diverse synthetic processes. The main purpose of this review is to present a survey of the scientific literature on levoglucosenone chemistry to provide an up-to-date on different stereoselective synthetic strategies for the construction of biologically important compounds, chiral inductors or templates for organic synthesis.

Bicyclic oxazines are attractive compounds and valuable synthetic intermediates as they can be easily obtained by hetero Diels-Alder reactions between cyclic dienes and nitroso dienophiles. In particular, the more strained case (i.e. the [2.2.1]-cycloadduct) represents an interesting powerful combination of stability and reactivity as it can be transformed into highly densely functionalized cyclopentene derivatives by a variety of ring-opening reactions. Aim of this article is to summarize the methods used by various chemists for opening of bicyclic oxazines by the formation of a new carbon-carbon bond, to give highly substituted ring systems containing multiple stereocenters. Particular emphasis will be given to regio- and stereoselective procedures, including the most recent developments on less strained [2.2.2]-cycloadduct.

Selective catalytic reduction of halogenated nitroaromatic compounds is the most widely used method for the synthesis of halogenated anilines, important intermediates in the chemistry of pesticides, herbicides, drugs, pigments and dyes. This review reports progress made in the last decade in the field of hydrogenation of halogenated nitro arenes with the use of heterogeneous catalysts. The first sections of the review contain a concise report on applications of halogenated anilines, methods for their preparation and reaction pathways for hydrogenation of haloaromatic nitro compounds. Subsequent sections discuss hydrogenation properties of platinum group metals, new catalysts based on gold and silver as well as nickel catalysts. Particular attention is paid to positive effects of the use of new unconventional supports and catalyst preparation methods. Finally, an attempt is made at systematising the most important factors affecting high activity and selectivity of heterogeneous catalysts for selective reduction of haloaromatic nitro compounds.

In 1881, Rainer Ludwig Claisen discovered a carbon-carbon bond-forming reaction between two esters or an ester and a carbonyl compound in the presence of a base. The reaction leads to β-keto esters or β-diketones respectively, and it was later named Claisen condensation, or classic Claisen condensation in the former case, and mixed (‘crossed’) Claisen condensation in the latter. The reaction now sits firmly in the repertoire of organic synthesis as one of the earliest name reactions. In continuing research, it became evident that the products of this aldol type reaction can be cleaved to produce starting materials. Namely, β-diketone moieties were reported to undergo the retro-Claisen reaction, which is β-dicarbonyl carbon-carbon bond cleavage. Although it was first described as a side, or even parasitic reaction, it was later incorporated into the body of carbon-carbon base-promoted cleavage reactions. Moreover, numerous recent reports have demonstrated the wide selection of methodologies that can be used in these transformations. The scope ranges from various base-mediated or acid-mediated reactions and biocatalyzed transformations, and it extends to recently discovered homogeneous catalyzed reactions. Interestingly, further synthetic applications of retro-Claisen reaction are now being realized, and this is reflected in syntheses of natural products and other fine chemicals. This reaction is nowadays a useful synthetic tool and this review surveys and consolidates the recent literature on the retro-Claisen reaction.

β-Carboline represents the core unit of several alkaloids and bioactive agents. This review assimilates the reports pertaining to the synthesis and applications of 1-formyl-9H-β-carbolines for affording 1-substituted, C-1-N-9 and C-1-N-2 fused β-carbolines.

Over the past twenty years benzo- and naphtho[b]furan synthesis has been a widely studied topic, certainly due to the presence of this structural unit in many biologically active compounds. Most of the known methods of the synthesis of these heterocycles are based on an intramolecular cyclization of various open-chain precursors. There are four possible ways of the cyclization and they are based on a formation of appropriate furan bonds: O-C2, C2-C3, C3-b and O-b. The following paper presents these four methods of synthesis of benzo[b]- and naphtho[b]furans which have been developed over the last years.

Chromones are an important group of heterocyclic compounds due to their important functions in nature and their pharmacological applications. Many efficient syntheses of chromones have been reported through the years but the search for novel methods addressing to the preparation of this type of compounds still remains a relevant topic. Simple and efficient procedures using molecular iodine for the synthesis of these organic molecules have been reported. The uses of catalytic amounts of iodine in cyclodehydration reactions and as additives in oxidative or photooxidative cyclizations are well known approaches for the preparation of new chromone-type compounds. The purpose of this review is to describe the most relevant work on chromone-type compounds using molecular iodine.

A one-pot synthesis of 7-amino-4-oxo-3-(2-(2-thienyl)vinyl)-4,8-dihydro-[1,2,4]triazino[3,4-b][1,3,4]thiadiazine-8- carbonitrile (2) via the reaction of 4-amino-3-sulfanyl-6-[2-(2-thienyl)vinyl]-1,2,4-triazin-5(4H)-one (1) with bromomalononitrile is described. The formation of the new fused heterobicyclic and heterotricyclic nitrogen systems ([1,2,4]triazino[3,4-b][1,3,4]thiadiazin-7- yl)guanidine 3, pyrimido[4,5-e][1,2,4]triazino[3,4-b][1,3,4]thiadiazin-4-one 5, [1,2,4]triazino[3,4-b][1,3,4]thiadiazin-7-ylcarbamodithioic acid 6, pyrimido[4,5-e][1,2,4]triazino[3,4-b][1,3,4]thiadiazin-4-one 8, [1,2,4]triazino[3,4-b][1,3,4]thiadiazin-7-ylformimidate 9, pyrido[2,3-e][1,2,4]triazino[3,4-b][1,3,4]thiadiazine-9-carbonitrile 11, (pyrimido[4,5-e][1,2,4]triazino[3,4-b][1,3,4]thiadiazin-8-yl) acetonitrile 12 and pyrimido[4,5-e][1,2,4]triazino[3,4-b][1,3,4]thiadiazine-4,10(10aH)-dione 13 was achieved by treating 2 with cyanamide, urea, thiourea, CS2 and ethanolic ethoxide, formamide, triethyl orthoformate, malononitrile, ethyl cyanoacetate and chloroacetyl chloride, respectively. Additionally, the 8-thiourea and 8-acetamide derivatives 16a,b, 18 and 19 were synthesized by reacting 2 with various isothiocyanate derivatives and acetic anhydride. The structures of all synthesized compounds were deduced by elemental analysis, mass spectrometry and analysis of their spectral data (IR, 1H NMR, 13C NMR).