Self-Assembly of 4,4'-Linked Dipyrromethanes from Unconventional ReactantsâPropargylamines, 2-(Vinyloxy)ethyl Isothiocyanate, and Alkylating Agents under Basic Conditions.
J Org Chem
; 89(2): 864-881, 2024 Jan 19.
Article
em En
| MEDLINE
| ID: mdl-38154056
ABSTRACT
Self-assembly of 4,4'-linked dipyrromethanes from 2-(vinyloxy)ethyl isothiocyanate, tertiary propargylamines, and alkylating agents has been discovered. The plausible reaction mechanism, the major stages of which have been confirmed experimentally, includes (1) the lithiation of propargylamine (with n-BuLi); (2) the formation of lithium N-[2-(vinyloxy)ethyl]but-2-ynimidothioate (product of the addition of monolithiated propargylamine to isothiocyanate); (3) isomerization of the latter in the corresponding allenylimidothioate (under the action of the t-BuOK/t-BuOH system); (4) low-temperature (<15 °C) intramolecular cyclization of the latter into potassium N-(5-amino-2-thienyl)-N-[2-(vinyloxy)ethyl]amide; (5) the base-induced cleavage of the C-O bond of the N-[2-(vinyloxy)ethyl] group and removal of vinyloxide-anion leading to acetaldehyde; (6) interaction of acetaldehyde with two molecules of N-(5-amino-2-thienyl)-N-[2-(vinyloxy)ethyl]amide-anion resulting in dithienomethane N-anionic intermediate; (7) recyclization of the latter into dipyrromethane S-anionic intermediate. Final S-alkylation affords synthetically challenging 4,4'-dipyrromethanes in a yield of 22-51%. The whole process is carried out in a single synthetic operation in a very short time (â¼10-15 min, excluding alkylation time).
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2024
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Article