Highly Efficient Regioselective Synthesis of 2‑Imino-4-oxothiazolidin-5-ylidene
Acetates via a Substitution-Dependent Cyclization Sequence under Catalyst-Free
Conditions at Ambient Temperature
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Abstract
A green
and efficient method for the synthesis of newer 2-imino-4-oxothiazolidin-5-ylidene
acetate derivatives under catalyst-free conditions by simply stirring
symmetrical and unsymmetrical 1,3-diarylthioureas with dialkyl acetylenedicarboxylates
in ethanol at room temperature has been developed. Interestingly,
the regioselective synthesis affords the 2-imino-4-oxothiazolidin-5-ylidene
acetate derivatives: the amine nitrogen bonded to an electron-withdrawing
substituent becomes part of the imino component, and the amine nitrogen
bonded to an electron-donating substituent becomes the heterocyclic
nitrogen. This is the first report wherein the impact of substituents
in directing the regiocyclization has been explained and the structure
conflict resolved by single-crystal X-ray analysis