Current Organic Synthesis - Volume 9, Issue 6, 2012

This review deals with the state-of-the-art techniques in non-enzymatic nucleic acid condensation from monomers. In particular, the procedures called monomer self-condensation and template-directed monomer condensation are described, which have been developed to achieve efficient synthesis of long nucleic acid polymers or to sequence-specifically amplify nucleic acid polymers, respectively. Starting from molecular requirements, details of the polymerization mechanisms and strategies are first presented and then compared. Finally, we discuss the relevance of these strategies to the investigation of possible early molecular information systems on the prebiotic earth and the development of novel synthetic methodologies for nucleic acids.

In this article we discuss synthetic routes to organic conjugated oligomers and polymers bearing triple C-C bonds that have been recently developed in our laboratories, based on Pd-catalyzed Csp-Csp2 coupling reactions. Experimental protocols have been tuned to face synthetic challenges such as the presence in the main conjugated backbone of multifunctional substituents or uncommon conjugated units. The relevance of the obtained products in terms of properties and applications is also shortly mentioned.

Iriomoteolides are novel macrolides possessing either a unique 15-membered or a 20-membered macrocycle, and displaying exceedingly potent cytotoxicity with IC50 values of up to 2 ng/mL. Thus far, over a period of about four years, ten research groups worldwide have published their synthetic efforts resulting in four total syntheses of iriomoteolides and a few diastereomers thereof, and a number of fragment and macrocyclic core syntheses. Interestingly, three total syntheses involved ring-closing metathesis as the key step for the construction of the macrocycle, whereas the synthesis of three fragments was accomplished using a cross-metathesis reaction. Herein we highlight assets and limitations of the olefin metathesis reaction in the synthesis of the title compounds.

Desymmetrization of prochiral compounds is one of the most efficient methods to obtain enantiomerically pure compounds (yield close to 100%); proof of this is its growing application over the last decade in the synthesis of key chiral intermediates used in the preparation of important biologically active compounds. Enzymes are highly specific, enantio- and regioselective catalysts that operate under relatively mild conditions and therefore represent an interesting alternative to chemical methods. This review describes significant progress, particularly from 2006 onwards, in enzymatic desymmetrization of prochiral compounds such as diesters, anhydrides, diamines and diols, where implementation of this strategy has allowed the design of new and improved synthesis routes, establishing it as one of the best alternatives for the preparation of optically active compounds.

Vinyl and aryl sulfonates are ubiquitous building blocks in organic chemistry, frequently exploited in the total synthesis of natural and non-natural products, due to their ease of formation and to their high reactivity, especially in metal-catalyzed cross-coupling reactions. The present review thus aims at first describing the classical and current methods to prepare these valuable synthons, with an emphasis on reaction mechanisms. The second part of the review aims at highlighting their main applications in organic synthesis, especially in the course of natural product total syntheses.

Aryl-fused 1,4-oxazepines and their corresponding oxo derivatives are structural components of a number of compounds exhibiting various biological activity. They were found to be useful as pharmaceuticals, for example as psychoneurotic, antihistaminic and analgesic agents. They are also known for relieving memory dysfunction such as that associated with reduced cholinergic function in Alzheimer's disease. Synthetic methods leading to the aryl-fused 2,3,4,5-tetrahydro-1,4-oxazepines can be classified into two groups. The first includes methods based on direct cyclization of the appropriate open-chain precursors, whereas the second involves methods based on the reduction of intermediate products which are usually adequate aryl-fused 2,3-dihydro-1,4-oxazepines, 4,5-dihydro-1,4- oxazepin-3-ones, 3,4-dihydro-1,4-oxazepin-5-ones, 1,4-oxazepin-3,5-diones. There are only a few methods of synthesis based on the transformation of chromanone. This paper presents a review of a variety of methods of the synthesis of important and potentially pharmacologically active 1,4-oxazepine derivatives.

This brief review deals with the recent progress in the implimentation of thio-Claisen rearrangement in synthetic organic chemistry. Thio-Claisen rearrangement has been utilized for the synthesis of many heterocyclic moieties of biological significance. Stereoselectivity of the thio-Claisen rearrangement has also been discussed. This short report mainly covers the literature published during 2003 onwards.

Compared with conventional batch-wise process, one-pot synthesis is the “condensation” of two or more steps into one-pot operation and increasingly used in chemical process research and development in order to achieve the desired molecular complexity in ecologically and economically efficient way. One-pot synthesis can be achieved via multicomponent reaction (MCR), cascade reaction, tandem reaction, or telescoping synthetic steps. This review summarizes recent progresses in this field, covering mainly four approaches developed for the application towards one-pot organic synthesis.

An efficient and regioselective one-pot direct synthesis of 4-vinyl-1,2,3-triazoles via cycloaddition of azides with propargyl alcohols and dehydration catalyzed by a CuCl/RuCl3.3H2O bimetallic catalysts in the presence of TFA (Trifluoroacetic acid) is developed.