Abstract
Two routes are reported for the synthesis of iminocyclobutenones having N-(het)aryl substitution: an addition/substitution sequence starting with cyclobutenediones and an aza-Wittig method. A new synthetic route to N-alkyl derivatives is also presented. This involves O-alkylation of 3-alkylamino-1,2-cyclobutenediones using Meerwein’s reagent and subsequent deprotonation under non-hydrolytic conditions. Lithium organyls were found to add to the remaining carbonyl group. The resulting tertiary alcohols undergo ring enlargement on heating in xylene to give 4-aminophenols, 4-amino-1-naphthols, or cyclopenta-annulated quinolines from 4-vinyl, 4-aryl, and 4-alkynyl derivatives, respectively.
Highlights
Cyclobutenones 1, containing an enone unit in a four-membered ring, combine ring strain with the well known enone reactivity.[1]
Attempts to expand the scope of the method for the synthesis of N-alkyl-iminocyclobutenones resulted in the isolation of the corresponding cyclobutenediones 2
This provides compounds for a broad-based study of the thermolyses of substituted iminocyclobutenes. These reactions show similarity to those of the analogous cyclobutenones. They are initiated by 4p-electrocyclic ring opening, followed by 6p-electrocyclic ring closure to give aminophenols or aminonaphthols
Summary
Cyclobutenones 1, containing an enone unit in a four-membered ring, combine ring strain with the well known enone reactivity.[1] Syntheses of these highly substituted derivatives are available, and these undergo facile electrocyclic ring opening to give conjugated ketene intermediates. 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
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