Abstract Until now, how the magnetic fields in M/X-class flaring active regions (ARs) differ from C-class flaring ARs remains unclear. Here, we calculate the key magnetic field parameters within the area of high photospheric free energy density (HED region) for 323 ARs (217 C- and 106 M/X-flaring ARs), including total photospheric free magnetic energy density E free , total unsigned magnetic flux Φ HED , mean unsigned current helicity h c , length of the polarity inversion lines L PIL with a steep horizontal magnetic gradient, etc., and compare these with flare/coronal mass ejection (CME) properties. We first show the quantitative relations among the flare intensity, the eruptive character, and Φ HED . We reveal that Φ HED is a measure for the GOES flux upper limit of the flares in a given region. For a given Φ HED , there exists the lower limit of F SXR for eruptive flares. This means that only the relatively strong flares with the large fraction of energy release compared to the total free energy are likely to generate a CME. We also find that the combinations of E free – L PIL and E free – h c present a good ability to distinguish between C-class and M/X-class flaring ARs. Using determined critical values of E free and L PIL , one predicts correctly 93 out of 106 M/X-class flaring ARs and 159 out of 217 C-class flaring ARs. The large L PIL or h c for M/X-class flaring ARs probably implies the presence of a compact current with twisted magnetic fields winding about it.
A stereoselective annulation protocol was developed to construct dihydrofuranoindoles from readily available starting materials. In the presence of a bifunctional squaramide, the Friedel-Crafts alkylation/annulation cascade process occurred smoothly to provide dihydrofuranoindoles in 26-95% isolated yields exclusively as trans-diastereomers (38-99% ee). This catalytic protocol was compatible with a range of structurally distinct hydroxyindoles bearing the hydroxyl group at different positions, providing four kinds of dihydrofuranoindoles. Moreover, gram-scale synthesis and further synthetic manipulation of the product were also demonstrated.
Abstract The protocol allows for the transformation of a broad range of enones, such as cinnamone derivatives, cyclic enones and chalcones including heterocyclic derivatives.
A [2 + 4]/[1 + 2] annulation approach was successfully established to construct pyrroloquinoline-fused cyclopropane in a highly diastereoselective fashion (>20:1 dr). The tetracyclic 1,7-fused indoles were efficiently obtained from readily available starting materials under mild conditions. This methodology displays impressive substrate generality with two reaction components. The products resulting from this doubly annulative strategy are useful synthetic intermediates.
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