Department of Biochemistry

As a part of the ‘bottom-up’ campaign for the precise preparation of carbon nanotubes, the chemical synthesis of carbon nanohoops is observing rapid progress, with a number of milestone achievements, over the past decade. With simple carbon nanohoops (e.g. cycloparaphenylenes) now no longer elusive targets, this Synpacts article highlights latest synthetic advances to further build up nanohoops’ π-systems. Works reviewed herein include the study explaining the unsuccessful Scholl reaction method, the preparation of a carbon nanohoop consisting solely of hexabenzocoronene units, syntheses of π-extended carbon nanohoops employing the ring-closing metathesis method, and the anthracene photodimerization/cycloreversion method for anthracene-incorporated carbon nanohoop synthesis.1 Introduction2 Some Latest Syntheses of π-Extended Carbon Nanohoops3 Conclusion

A palladium-catalyzed regioselective ortho-halogenation of 2-pyridyl sulfoxides via a C–H activation pathway has been reported. Under the conditions established, this reaction proceeded smoothly and could tolerate a variety of functional groups under mild conditions.

Asymmetric catalytic activities of various organocatalysts bearing double hydrogen-bonding donor units showing different pK
a values were examined for direct aldol reactions of cyclohexanone with aromatic aldehydes. Organocatalyst with motif exhibiting the highest acidity resulted in the corresponding aldol products with the highest enantioselectivity. A good correlation has been observed between the asymmetric catalytic activity for direct aldol reactions and acidities of double hydrogen-bonding donating units.

A route to the oxabicyclic cores of the HIV cytoprotective quinolone alkaloids, waltheriones C and D, is described. The approach relies on a stereospecific transannular bromoetherification followed by reductive debromination. The route can also be rendered enantioselective via enzymatic reduction of a key intermediate (>99:1 er).

A domino reaction sequence has been evaluated that begins with union of novel dihydrooxazinone precursors with 2-alkynyl-substituted benzaldehyde components through aldol condensation. Ensuing operations, including alkene isomerization, Diels–Alder, and retrograde Diels–Alder with loss of CO2 occurs in the same reaction vessel to provide polysubstituted tricyclic pyridine products.

A Sc(OTf)3-catalyzed reaction of vinyl azides with donor–acceptor cyclopropanes affords highly functionalized azidocyclopentanes in a diastereoselective fashion. The resulting azidocyclopentanes could be transformed into various cyclic scaffolds.

Iminophosphoranes reacted with CS2 at –5 °C to produce the isothiocyanates, which were treated with primary amine to give thioureas in 73–91% yields. The subsequent reaction of thioureas with alkyl bromides in the presence of solid K2CO3 produced 2-alkylthiopyrimidin-4(3H)-ones in 68–88% yield via tandem intramolecular cyclization–isomerization–S-alkylation.

The first enantioselective decarboxylative aldol addition with α-amido-substituted malonic acid half oxyesters (MAHOs) is described. The combined use of a newly designed bifunctional sulfonamide catalyst with pentafluorobenzoic acid as an additive afforded the β-hydroxy-α-amino acid derivatives in moderate to high yields and with high enantioselectivities.

A palladium-catalyzed three-component coupling reaction of 2-fluoroallylic acetates with phenols, and imides is disclosed. The reaction was effectively catalyzed by [Pd(C3H5)Cl]2/DPPF in the presence of Cs2CO3, and phenols and imides were introduced onto the allyl unit through the C–F bond activation. Furthermore, the reaction proceeds with both high regioselectivity and high Z-selectivity.