An enantioselective synthesis of spiropyrazolone-fused cyclopenta[c]chromen-4-ones is demonstrated via a (3+2) cycloaddition reaction. The reactions of 3-homoacylcoumarins and α,β-unsaturated pyrazolones in the presence of the cinchonaalkaloid derived hydrogen-bonding catalyst provide aforementioned spiropyrazolone-chromenone adducts bearing five contiguous stereocenters, of which one is the spiro all-carbon quaternary stereocenter in high yields (up to 98%) with good to excellent stereoselectivities (>25:1 dr and up to 99% ee). This one-pot methodology could also be practically demonstrated on a gram-scale with similar efficacy.
Because of its unsaturated bonds, C 60 is susceptible to polymerize into dimers. The implications of nitrogen doping on the geometrical and electronic structure of C 60 dimers have been ambiguous for years. A quarter-century after the discovery of azafullerene dimer (C 59 N) 2 , we reported its single crystallographic structure in 2019. Herein, the unambiguous crystal structure information of (C 59 N) 2 is elucidated specifically, revealing that the inter-cage CC single bond length of (C 59 N) 2 is comparable with that of an ordinary C(sp 3)-C(sp 3) single bond, and that the most stable conformer of (C 59 N) 2 is gauche-conformer with a dihedral angle of 66°. To amend the structural deviations, geometrical structure of (C 59 N) 2 is optimized by a B3LYP-D3BJ function, which is proved to be more consistent with its single crystal structure than those by the commonly used B3LYP function. Moreover, the calculation method is also suitable for other representative fullerene dimers, such as (C 60) 2 and its divalent anion. Additionally, the dissociation of (C 59 N) 2 at 473 K under mass spectrometric conditions suggests the inter-cage CC bond is relatively weaker than an ordinary CC single bond, which can be explained by the interaction energies of inter-cages.
We report a phosphine-mediated direct βacylation of α,β-unsaturated 1,3-diketones with acyl chlorides and a base. Functionalized furanones were also prepared by the reaction of cinnamic acid and acyl chloride according to our protocol via β-acylation. Our studies revealed that α,βunsaturated 1,3-diketones with an electron-donating group at the second position favor the formation of β-acylated products, whereas those with oxygen, such as anhydrides, favor furanones via an unprecedented C-acylation/cyclization sequence.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.