New Access to the Synthesis of 1,1,4,4-Tetracyanobuta-1,3-Diene-Based Push–pull Chromophores Using Tetracyanoethylene Oxide via [3+2] Cycloaddition-Ring Opening Reactions

Herein we report a new way to access the synthesis of established invaluable push–pull chromophores based on 1,1,4,4-tetracyanobuta-1,3-dienes (TCBDs) using tetracyanoethylene oxide (TCNEO) upon reaction with alkynes substituted with an electron-donating group (EDG) via [3+2] cycloaddition (CA) followed by ring-opening (RO) reactions. Further, we uncovered that the facile [3+2] CA–RO reaction under simpler reaction condition is possible due to the presence of EDG group, otherwise, even the formation of [3+2] cycloadduct without EDG requires harsher condition and does not lead to TCBD as reported earlier in 1965 by Linn and Benson.