The Chemistry of Phenylcyclobutenediones

Abstract

Phenylcyclobutenediones are easily obtainable and very stable. Depending on the nature of the substituent R in position 3, they may be formally regarded as vinylogous carboxylic acid derivatives (Rhalogen, OCH3, OH, SH) or as α,β‐unsaturated diketo compounds (RH, alkyl, aryl). Their behavior in reactions justifies this approach. Ring contraction, ring expansion, and ring cleavage reactions are described.

New Convenient One-Pot Methods of Conversion of Alkynes to Cyclobutenediones or α,β-Unsaturated Carboxylic Acids Using Novel Reactive Iron Carbonyl Reagents

“…For the cyclobutenedione 2a , HRMS data were also obtained. e The spectral data of product 7a (IR, NMR) were identical to the data reported for this compound 17a. The spectral data of product 10a are comparable to the spectral data reported for the cyclobutenedione 7a .…”

New Syntheses and Ring Expansion Reactions of Cyclobutenimines

“…[14][15][16] There are also scattered examples of cyclobutenimine derivatives in the literature. For example, cyclobuta[e]triazines 6 and cyclobuta[c]quinoxalinones 7 were obtained when cyclobutenediones 2 were treated with the corresponding nitrogen biselectrophiles such as amidrazones [17][18][19] or 1,2-diaminobenzenes, respectively. [18][19][20][21] Semisquaric acid derivatives yield cyclobutenone hydrazones 8 upon treatment with arylhydrazones [19] and cyclobutenone oximes are available by aza-Wittig monoimination of cyclobutendiones.…”

“…For example, cyclobuta[e]triazines 6 and cyclobuta[c]quinoxalinones 7 were obtained when cyclobutenediones 2 were treated with the corresponding nitrogen biselectrophiles such as amidrazones [17][18][19] or 1,2-diaminobenzenes, respectively. [18][19][20][21] Semisquaric acid derivatives yield cyclobutenone hydrazones 8 upon treatment with arylhydrazones [19] and cyclobutenone oximes are available by aza-Wittig monoimination of cyclobutendiones. [22] The reaction of squaric or semisquaric acid derivatives with aromatic amines gives zwitterionic compounds, [9,23,24] e.g., 9 [23] (Scheme 2).…”