Abstract
Triethylborane-initiated atom transfer radical cyclization reactions of various allyl or 3-butenyl iodoacetates could be efficiently carried out at room temperature with trifluoroacetic acid as the solvent. Compared to water as the solvent, trifluoroacetic acid has better solubility for organic substrates and might also function as an acid catalyst.
Highlights
The past two decades have witnessed a rapid growth in intramolecular free radical cyclization reactions and their application in organic synthesis.[1,2,3,4,5,6,7,8,9]
In order to have efficient cyclization, fast tautomerism between s-trans and s-cis rotomers of the α-ester radicals is essential because the cyclization requires the s-cis conformations of higher energy
Oshima and coworkers showed that water is a powerful solvent for atom transfer radical cyclization reactions.[13,14]
Summary
The past two decades have witnessed a rapid growth in intramolecular free radical cyclization reactions and their application in organic synthesis.[1,2,3,4,5,6,7,8,9] Cyclization[10] of α-carbonyl radicals leading to the formations of lactones, lactams, and cycloalkanones has received considerable attention because of its great potential in natural product synthesis. Oshima and coworkers showed that water is a powerful solvent for atom transfer radical cyclization reactions.[13,14] As a result, reaction of 1a in water (0.03 M) at room temperature gave the expected cyclization product 2a in 67% yield. We report that trifluoroacetic acid act as an excellent co-solvent for the atom transfer cyclization reactions in water.
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