The Aromaticity of the Stannole Dianion

Abstract

In the last decade, much attention has been focused on the anions and dianions of siloles [1] and germoles, [1f, 2] which are heavier congeners of the cyclopentadienyl anion.[3] The degree of aromaticity of silolyl anions depends on the substituent, [1b,f] while the germolyl anions do not show aromaticity because the negative charge is localized on the germanium atom. [1f, 2a,2c] In contrast, the negative charges in the dianions of siloles and germoles are significantly delocalized in the C 4 M (M = Si, Ge) ring and they were concluded to be aromatic. [1d-f, 2b,2d,2e, 4] The aromatic delocalization in these dianions was evidenced by NMR studies, calculations, and Xray crystal structural analyses, which showed no alternation of the CÀC bonds within the ring. In contrast to the wellinvestigated mono-and dianions of siloles and germoles, neither mono-nor dianions of stannoles had been reported before we undertook a study of such species a few years ago.

New Reactions of a Dibenzo[a,e]pentalene

“…In the 7 Li NMR spectrum, an upfield resonance was observed at d = À7.4 ppm, which suggested that the anionic moiety of 5 should be highly aromatic. [9] The carbon atom at the 9-position of some fluorenyllithiums was reported to resonate at about d = 80 ppm. [10] Likewise, in the 13 C NMR spectrum, a 13 C signal at d = 80.47 ppm can be assigned to a carbon atom at the 1-position in the anionic moiety of 5.…”

“…The intensity data were collected at À170 8C on a Bruker SMART APEX equipped with a CCD area detector with graphite-monochromated Mo Ka radiation (l = 0.71073 ) and graphite monochromater. Formula = C 55 H 93 LiO 9 Reaction of dibenzopentalene 3 with bromine: Bromine (0.22 mL, 4.27 mmol) was added to an ether (10 mL) solution of dibenzopentalene 3 (108.7 mg, 0.21 mmol) at room temperature and the resulting mixture was stirred for 6 h. After addition of saturated aqueous sodium sulfite to the reaction mixture, the organic layer was extracted with ether, dried over anhydrous magnesium sulfate, and concentrated to give a crude product (173.9 mg). The residue was chromatographed on silica gel (hexane) to afford 5,10-dibromodibenzoA C H T U N G T R E N N U N G [a,e]pentalene (8) (54.1 mg, 71 %).…”

Synthesis, Structure, and Reactivity of Lewis Base Stabilized Plumbacyclopentadienylidenes

“…[1,2] For the last decade, much attention has been focused on the investigation of whether aromaticity is maintained or changed by the introduction of heavier Group 14 atoms into p-frameworks. [3,4] Very recently, we have succeeded in the synthesis of dilithioplumbole, which has considerable aromatic character, thus clarifying that incorporating a lead atom into the carbon p-framework does not disrupt its aromaticity.…”

Titanium–Salan‐Catalyzed Asymmetric Epoxidation with Aqueous Hydrogen Peroxide as the Oxidant

“…[2] In particular, much effort has been directed toward the development of a chiral catalyst for epoxidation because of the high utility of optically active epoxides as versatile chiral building blocks. [3,4] However, a general and highly enantioselective epoxidation of unfunctionalized olefins with hydrogen peroxide has not been developed.Recently, we developed a chiral di-m-oxo titanium-salalen (salalen [5,6] : hybrid salan/salen tetradentate (ONNO)-type ligand; salan: N,N,-bis(o-hydroxybenzyl)-1,2-diaminoethane, salen: N,N-bis(salicylidene)ethylenediamine) complex that was able to catalyze the epoxidation of unfunctionalized olefins using aqueous hydrogen peroxide with high enantioselectivity and a high turnover number of the catalyst. [7] The robustness and the unique catalysis of the titanium-salalen complex are in marked contrast with the ineffectiveness of the corresponding di-m-oxo titanium-salen complex as an epoxidation catalyst.…”