Photolytic, Thermal, Addition, and Cycloaddition Reactions of 2-Diazo-5,6- and -3,8-disubstituted Acenaphthenones

Spirocyclizations Involving Oxonium Ylides Derived from Cyclic α-Diazocarbonyl Compounds: An Entry into 6-Oxa-2-azaspiro[4.5]decane Scaffold

New types of cyclic diazo compounds capable of Rh(II)-catalyzed spirocyclizations with tetrahydrofuran have been discovered. The formation of the spirocyclic framework is thought to proceed via the formation of Rh(II) carbene species followed by interaction with the Lewis basic oxygen atom of tetrahydrofuran to give oxonium ylide species. The latter evolves predominantly via the Stevens type rearrangement leading to an [n + 1] ring expansion of the tetrahydrofuran moiety, which results in the formation of a medicinally relevant 6-oxa-2-azaspiro[4.5]decane scaffold. The spirocyclization process was often observed in competition with mechanistically distinct C-H insertion into a tetrahydrofuran molecule. This competing process gave compounds based on the 3-(tetrahydrofur-2-yl)pyrrolidine scaffold, which are also relevant from the medicinal chemistry standpoint. These findings enrich the available arsenal of metal-catalyzed spirocyclization methods based on the use of cyclic diazo compounds.

Recent developments in photochemical reactions of diazo compounds

Chemistry of diazo compounds is dominated by transition metal catalysis but recently, photoinitiated reactions of diazo compounds have attracted a lot of attention. This mini-review describes recent discoveries on the reactivity of diazo compounds under light irradiation.

Phosphine-catalyzed domino reactions of alkynyl ketones with sulfonylhydrazones: construction of diverse pyrazoloquinazoline derivatives

An efficient method for the synthesis of C-1 position acyl substituted pyrazoloquinazoline derivatives via a PBu₃-promoted domino process of sulfonylhydrazones and alkynyl ketones was developed.

Syntheses and photophysical properties of 5'-6-locked fluorescent nucleosides

Nine fluorescent 5'-6-locked nucleosides were synthesized by condensation of various 1,2-diketones with 5-amino-2'-deoxycytidine. The nucleosides have different substituents on the pyrazine core structure, ranging from two methyl groups to polyaromatic rings. The photophysical properties of each nucleoside were determined, with the nucleosides displaying diverse absorption and emission maxima, extinction coefficients and quantum yields. The nucleoside with the highest fluorescence brightness was phosphitylated and incorporated into an oligonucleotide by means of automated oligonucleotide synthesis. The labelled oligonucleotide in aqueous buffer exhibited a substantially lowered extinction coefficient and quantum yield compared to the nucleoside in THF. The photophysical properties of the nucleoside were also compared in different DNA structural contexts, a single strand, a 14-mer duplex, a 14-mer duplex with an 11-mer overhang, and a 25-mer nicked duplex labelled at the nick site. Circular dichroism and melting temperature studies verified that the nucleoside did not perturb or destabilize the DNA helixes. In fact, when incorporated at the nick site, the nucleoside was found to stabilize the nicked duplex notably compared to its unmodified counterpart. The brightness of the fluorescent nucleoside in DNA increased as the polarity of its surroundings decreased, being highest in the 25-mer nicked duplex where exposure to the polar solvent is minimized by stacking to the adjacent bases on both the 3'- and 5'-side. The nucleosides brightness in the nicked duplex was also found to increase with lowered temperature, in accordance with expected temperature-dependent changes in the stacked-unstacked equilibrium at the nick site.