Äthinierungsreaktionen, III. Umsetzung von Chinonen mit Acetylen

Abstract

Die Anlagerung von Acetylen a die Carbonylgruppen von Chinonen mittels Alkaliacetyliden in flüssigem Ammoniak führt zu den entsprechenden Dichinolen. 2‐Methyl‐substituierte 1–4‐Chinone reagieren unter den Versuchsbedingungen jedoch im allgemeinen nur zu Monochinolen. Das vom p‐Benzochinon abgeleitete Acetylen‐Anlagerungsprodukt ist in neutralem Medium beständig, zeichnet sich aber in saurem Medium durch seinen leichten Übergang in verschiedene aromatische Verbindungen aus.

Reductive Aromatization/Dearomatization and Elimination Reactions to Access Conjugated Polycyclic Hydrocarbons, Heteroacenes, and Cumulenes

“…Similar to the halogenated acids, dilute H 2 SO 4 , dilute AcOH, and concentrated HCO 2 H (formic acid) all furnish the trisubstituted benzene 3 . Thus, it appears that the counteranion does not influence the reaction.…”

“…After screening several reducing agents, such as Na 2 S 2 O 4 (sodium dithionite), NaH 2 PO 2 , and HI, they found SnCl 2 in AcOH to be the best choice for the aromatization of the 9,10‐bis(ethynyl)anthracene‐9,10‐diol. The aromatization of other compounds, including various ortho ‐ and para ‐substituted benzene, naphthalene, and anthracene derivatives soon followed –. Ried and co‐workers extended the use of SnCl 2 in acetic acid to the reduction of 9,10‐bis(phenylethynyl)anthracene‐9,10‐diol into 9,10‐bis(phenylethynyl)anthracene .…”

“…Conversely, para ‐diethynyldiols 1 readily react in diluted strong acids, mainly due to their tendency to transform into energetically favored aromatic structures. Treatment with HCl, for instance, will convert diol 1 (R = H) into chloroacetophenone 2 (X = Cl), via a modified Rupe rearrangement . Addition of diluted HCl to other alkynols (e.g., 1 , R = alkyl) furnishes two isomeric products, namely alcohol 3 (as a result of a vinylogous pinacol rearrangement) and a product assumed to be an endo‐ether (not shown) .…”

“…Thus, it appears that the counteranion does not influence the reaction. Catalytic hydration with Raney‐Ni or Pd/C transforms diol 1 (R = H) either into the saturated cyclohexane derivative 6 or the aromatized hydroquinone 7 , respectively . The para ‐bis(phenylethynyl)cyclohexadiendiol 1 (R = Ph), however, yields para ‐substituted benzene 8 and small amounts of the saturated cyclohexane 6 independent of the catalyst used …”

(Z)-3,6-Diethynyl-3,6-dihydroxycyclohexa-1,4-diene

“…Although the synthesis of the diol has been reported in 30±45% yield (Ried & Schmidt, 1957), we adopted a two-step strategy reported by Srinivasan et al (2003) with 85±90% overall yield starting from pbenzoquinone. Addition of two equivalents of lithium trimethylsilyl acetylide in dry tetrahydrofuran to p-benzoquinone at 195 K and subsequent warming of the reaction mixture to room temperature furnished the diol as a mixture of Z and E isomers in the ratio 1:2.…”