Stereocontrolled Access to Benzo-Annelated all-cis- andcis,cis,cis,trans-[5.5.5.6]Fenestranones and all-cis-[5.5.5.5]Fenestranes

A triple cascade approach towards the diastereoselective synthesis of spiro trans-decalinol scaffolds

A [2+2+2] annulation reaction between cyclohexanone, β-nitrostyrene and 2-arylidene-1,3-indanedione afforded multisubstituted spiro trans-decalinol derivatives in high chemical yields (up to 75%) and excellent diastereoselectivity (up to >20 : 1) at room temperature. This one-pot three-component system follows a triple cascade sequence via the Michael/nitro-Michael/Aldol process, resulting in the formation of three C-C bonds, five contiguous stereocenters as well as a spiro quaternary carbon center.

Enantiopure Aromatic Saddles Bearing the Fenestrindane Core

The synthesis of enantiomerically pure, configurationally stable fenestrindane-based polyaromatic compounds with saddle-like structures is reported. Seven racemic fenestrane synthetic precursors were first screened by chiral HPLC for resolvability into enantiomers. Among the three resolvable precursors, a tribenzofenestrene derivative was resolved on a semipreparative scale, and the absolute configuration of the more slowly eluting enantiomer was established by X-ray crystallography. The enantiopure tribenzofenestrenes were then separately converted, in six steps, to the saddle-shaped fenestrindane derivatives in optically pure form. The two enantiomeric pairs of saddles were characterized by ¹H and ¹³C NMR spectroscopy, mass spectrometry, and circular dichroism spectroscopy. All new compounds reported herein represent the first enantiopure non-natural carbocyclic fenestranes isolated to date.

From Fenestrindane towards Saddle-Shaped Nanographenes Bearing a Tetracoordinate Carbon Atom

Two saddle-shaped polycyclic aromatic compounds (8 a and 8 b) bearing an all-cis-[5.5.5.5]fenestrane core surrounded by an o,p,o,p,o,p,o,p-cyclooctaphenylene belt were synthesized and characterized by NMR spectroscopy and mass spectrometry. The key step of this synthesis involves the formation of four cycloheptatriene rings from the corresponding electron-rich 1,4,9,12-tetraarylfenestrindane derivatives 7 a and 7 b in Scholl-type cyclizations. The structural details of the D_2d -symmetric saddle compound 8 a were determined by X-ray crystallography, and the properties of 8 a and 8 b were studied by UV/Vis and fluorescence spectroscopy and cyclic voltammetry.