Dianion and Tetraanion Octalene

Abstract

amine (13 b j afforded 8.5% trans-I-bromo-2-methoxymethylcyclopropane (14 b ) .The trans-amines (1 3 a, b ) yielded only traces of cyclopropyl bromides. This finding is consistent with a substitution with inversion, which in the case of the trans-diazonium ions is sterically hindered by the 2-substituents, so that it can no longer compete with ring cleavage.-The allyl alcohols (1 2)-OH and (15)-(OH) are formed stereospecifically via disrotation. The corresponding allyl bromides (X=Br) are not configurationally stable.Our results refute-at least for nitrogen as leaving g r o u p the concept of a retentive SN2-substitution at the cyclopropane ring. Retention of configuration is only observed when the disrotatory cyclopropyl-ally1 rearrangement is initiated, but cannot be led to completion owing to opposing ring strain; in these cases partly opened cyclopropyl cations are probably involved as intermediates. In the case of unconstrained ring cleavage the competing substitution at cyclopropanediazonium ions proceeds with inversion.

A Chemiluminescent Tetraaryl Diborane(4) Tetraanion

“…[37] [3] 4À accumulates ah igh negative charge on ar elatively small molecule.T etraanionic organoboranes are as yet unknown and even remotely comparable species hosting such high charge density are rare. [38] Herein we report an optimized high-yield synthesis of the tetraanion salt Na 4 [3]and provide amechanistic proposal for its formation. Na 4 [3]i su nique among all other organoboron compounds in that it emits intense blue light upon contact with ambient air, thus representing an entirely new class of chemiluminescent molecules.T he controlled two-electron oxidation of Na 4 [3]g ives the 9,9'-bis(borafluorenylidene) Na 2 [3], ad oubly boron-doped analogue of compound B and an important but previously elusive isomer of [2] 2À .F actors that trigger the skeletal rearrangement of [3] 2À to [2] 2À are elucidated and juxtaposed with the conditions under which the widely investigated isomerization of the carbonaceous B/C couple occurs.…”

Pyrrole‐Bridged Porphyrin Nanorings

“…Annulenoannulenes that consist of multi-annulated aromatic annulenes have been extensively investigated in terms of their possible overall aromaticity. [11] In these three cases, the central resonance contributors (shown in gray in Scheme 1) correspond to socalled expanded isophlorins. Isophlorin (N,N'-dihydroporphyrin) is a reduced 20 p-electron congener of porphyrin, in which the macrocyclic conjugation surrounds the carbon periphery.…”