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Highly Z-selective synthesis of 1,3-oxathiol-2-ylidenes and 4-methylene-oxazolidine-2-thiones via atom-specific 5-exo-dig cyclization of propargyl alcohol with isothiocyanate

S. Antony Savarimuthu, Leo Prakash Orcid Logo, S. Augustine Thomas, Thirumanavelan Gandhi, Mrinal K. Bera

Organic & Biomolecular Chemistry, Volume: 18, Issue: 18, Pages: 3552 - 3562

Swansea University Author: Leo Prakash Orcid Logo

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DOI (Published version): 10.1039/d0ob00083c

Abstract

DBU mediated 5-exo-dig cyclization of isothiocyanate and propargyl alcohol leading to valuable heterocyclic compounds has been accomplished. The different modes of nucleophilicity (either S-selective or N-selective) of isothiocyanates were found to depend on the substitution pattern of propargyl alc...

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Published in: Organic & Biomolecular Chemistry
ISSN: 1477-0520 1477-0539
Published: Royal Society of Chemistry (RSC) 2020
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URI: https://cronfa.swan.ac.uk/Record/cronfa54303
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Abstract: DBU mediated 5-exo-dig cyclization of isothiocyanate and propargyl alcohol leading to valuable heterocyclic compounds has been accomplished. The different modes of nucleophilicity (either S-selective or N-selective) of isothiocyanates were found to depend on the substitution pattern of propargyl alcohol. The terminal propargyl alcohol and isothiocyanate underwent an N-nucleophilic attack to afford 3-substituted 4-methylene oxazolidine-2-thiones. In contrast, exclusive S-nucleophilic cyclization was observed with internal propargyl alcohol to produce (Z)-1,3-oxathiol-2-ylidenes and (Z)-N-(Z)-4-ethylidene-1,3-oxathiolan-2-ylidenes from secondary and primary propargyl alcohols, respectively. The formation of high Z-selectivity in the imine motif and alkene is the highlight of this new method as multiple selectivities over C[double bond, length as m-dash]N and C[double bond, length as m-dash]C in a single system are synthetically highly challenging. The Z-selectivity in imine and alkene may be attributed to electronic and steric factors respectively.
Issue: 18
Start Page: 3552
End Page: 3562

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