TY - JOUR
T1 - Single-step microwave-mediated synthesis of oxazoles and thiazoles from 3-oxetanone
T2 - a synthetic and computational study
AU - Orr, David
AU - Tolfrey, Alexandra
AU - Percy, Jonathan
AU - Frieman, Joanna
AU - Harrison, Zoe A
AU - Campbell-Crawford, Matthew
AU - Patel, Vipulkumar K
PY - 2013/7/15
Y1 - 2013/7/15
N2 - The direct microwave-mediated condensation between 3-oxetanone and primary amides and thio-amides has delivered moderate to good yields of (hydroxymethyl)oxazoles and (hydroxymethyl)thiazoles. The reactions use a sustainable solvent and only require short reaction times. These are highly competitive methods for the construction of two classes of valuable heteroarenes, which bear a useful locus for further elaboration. Electronic structure calculations have shown that the order of events involves chalcogen atom attack at sp3 carbon and alkyl–oxygen cleavage. The critical role of acid catalysis was shown clearly, and the importance of acid strength was demonstrated. The calculated barriers were also fully consistent with the observedorder of thioamide and amide reactivity. Spontaneous ring opening involves a modest degree of CO cleavage, moderating the extent of strain relief. On the acid-catalysed pathway, CO cleavage is less extensive still, but proton transfer to the nucleofuge is well advanced with the carboxylic acid catalysts, and essentially complete with methanesulfonic acid.
AB - The direct microwave-mediated condensation between 3-oxetanone and primary amides and thio-amides has delivered moderate to good yields of (hydroxymethyl)oxazoles and (hydroxymethyl)thiazoles. The reactions use a sustainable solvent and only require short reaction times. These are highly competitive methods for the construction of two classes of valuable heteroarenes, which bear a useful locus for further elaboration. Electronic structure calculations have shown that the order of events involves chalcogen atom attack at sp3 carbon and alkyl–oxygen cleavage. The critical role of acid catalysis was shown clearly, and the importance of acid strength was demonstrated. The calculated barriers were also fully consistent with the observedorder of thioamide and amide reactivity. Spontaneous ring opening involves a modest degree of CO cleavage, moderating the extent of strain relief. On the acid-catalysed pathway, CO cleavage is less extensive still, but proton transfer to the nucleofuge is well advanced with the carboxylic acid catalysts, and essentially complete with methanesulfonic acid.
KW - annulation
KW - density functional calculations
KW - microwave chemistry
KW - nitrogen heterocycles
KW - sulfur heterocycles
UR - http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1521-3765
U2 - 10.1002/chem.201301011
DO - 10.1002/chem.201301011
M3 - Article
SN - 0947-6539
VL - 19
SP - 9655
EP - 9662
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 29
ER -