Chemical Science Blog

Incorporating selenium into a polymer backbone can improve the polymer’s electron transport and could lead to improved organic electronics, reports scientists from the UK and Australia.

Ambipolar conjugated polymers, which can transport both holes and electrons, are of great interest as a method to mimic silicon-based logic circuits. Thiophene copolymers have been shown to be good hole transporters but are let down by their ability to transport electrons. 

Replacing thiophene with selenophene results in a significant reduction in polymer band gap, enabling the polymers to effectively transport electrons as well as holes. The resulting polymers display one of the highest hole mobilities reported for any device structure.

Download the Chemical Science Edge article to find out more.

Huw Davies’ group have developed a domino sequence for the asymmetric synthesis of highly functionalised cyclopentanes.

The researchers from Emory University have combined scandium catalysis with a previously reported asymmetric rhodium-catalysed dienol formation to afford cyclopentanes in good to excellent levels of enantioselectivity. Four new stereogenic centres are formed in the reaction sequence and the cyclopentane products are obtained as single diastereoisomers.

The one-pot procedure commences with a tandem oxygen ylide formation and [2,3] sigmatropic rearrangement between racemic allyl alcohol 1 and vinyl diazoacetate 2, resulting in formation of chiral dienol 4. Upon heating, an oxy-Cope rearrangement provides enol 5 in quantitative yield albeit with slight erosion of enantiomeric excess. Subsequent tautomerisation yields ketone 6, which is primed for a scandium triflate-catalysed carbonyl ene reaction on elevation of temperature, affording the cyclopentane product.

The impressive diastereoselectivity of this reaction combined with the complexity of the enantioenriched cyclopentane products highlights the synthetic power of reactive metal carbenoids in such thoughtfully designed reaction sequences. Download Davies’ Edge article to find out more.

 Posted on behalf of Alice E. Williamson, Chemical Science web writer.

Researchers have shown that acid-catalysed condensations of aminobenzaldehydes with indole result in the formation of different products depending on whether the aminobenzaldehyde is primary or secondary.

Daniel Seidel’s group at Rutgers, The State University of New Jersey, found that N-methylbenzaldehyde reacts with indole to form neocryptolepine-related structures in a single step. Neocryptolepine (5) and its analogues are attractive targets for synthesis as they display promising antimalarial activity.

Conversely, primary benzaldehydes such as aminobenzaldehyde react under similar conditions to form quinolines (7). The mechanistic pathways leading to the formation of both indoles (5) and quinolines (7) are initially identical, with aminobenzaldehyde 1 condensing with indole 2 to form the corresponding azafulvenium ions (3), which undergo ring closure to yield tetracyclic products (4). At this point the mechanisms diverge; secondary systems (4a) undergo proton loss and oxidation to give neocryptolepine analogues (5), whilst primary systems (4b) undergo proton transfer to give products of type 6, which aromatise to form quinoline products (7) on ring opening.

The group made a range of both neocryptolepine analogues and quinoline systems in good to excellent yields, representing important scaffolds for medicinal chemistry.

Seidel’s Edge article is free to download. Let me know what you think of this work by leaving your comments below.

Posted on behalf of Alice E. Williamson, Chemical Science web writer.

Researchers from the University of Delaware have reported a total synthesis of hyacinthacine A2, an attractive target owing to its selective glycosidase inhibition and activity against HIV. 

Joseph Fox’s research group achieved the synthesis in less than ten steps from sucrose by designing and synthesising a functionalised 5-aza-cyclooctene system (1) that would undergo a novel transannular hydroamination, following stereocontrolled photoisomerisation.

The efficiency of the photoisomerisation process was improved by using a flow system that removes trans-isomers by selective complexation with silver salts, thereby enabling the cis-isomer of 1 to be recycled. Incorporation of a fused acetonide ring system in 1 imposed significant conformational constraints to favour formation of the desired trans-diastereosiomer 2 in good yield and in 8:1 diastereomeric ration following decomplexation from the silver salts.

Following separation of the major diasteroisomer of 2, and cleavage of both trifluoroacetyl and acetonide protecting groups, the corresponding ammonium salt was obtained. The planar chirality present in 2 was perfectly transferred in a transannular hydroamination to give the point chirality present in the natural product.

Find out more by downloading Professor Fox’s Chemical Science Edge article, which is free to access.

Posted on behalf of Alice E. Williamson, Chemical Science web writer.