Preparation and Cycloaddition Reactions of Oxazoline Nitrogen Oxides

Oxazoline N-oxides have been prepared in medium to high yields under mild conditions by condensation of 2-(hydroxyamino)-2-methyl-1-propanol with ortho esters or amide acetals. 3 + 2 Cycloaddition reactions of the oxazoline N-oxides and the related pyrroline N-oxides with phenyl isocyanate, dimethyl acetylenedicarboxylate, methyl phenylpropiolate, phenylpropiolonitrile, methyl acrylate, and acrylonitrile were carried out. The reaction of 4,4-dimethyl-2-phenyloxazoline N-oxide with acetylenic dipolarophiles in concentrated solutions of dimethylamine hydrochloride in dichloromethane, however, led to the formation of isoxazoles. Competitive experiments demonstrated that 2,4,4-trimethyloxazoline N-oxide is at least 6,800 times more reactive toward phenyl isocyanate than the analogous 2,5,5-trimethylpyrroline N-oxide, and is 160 times more reactive toward dimethyl acetylenedicarboxylate than the pyrroline N-oxide. Rate constants for the 3 + 2 cycloaddition reactions of 4,4-dimethyl-2-phenyloxazoline N-oxide and 5,5-dimethyl-2-phenylpyrroline N-oxide with phenyl isocyanate and dimethyl acetylenedicarboxylate were measured. These data indicate that the oxazoline N-oxide is approximately 76,000 times more reactive toward phenyl isocyanate than the pyrroline N-oxide, and is 70 times more reactive toward dimethyl acetylenedicarboxylate than the pyrroline N-oxide. An explanation for the enhanced reactivity of oxazoline N-oxides is forwarded on the basis of frontier molecular orbital theory.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Ashburn, Stephen Patrick

• Chemistry, Organic

Identifier

(UMI)AAI8511575

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/70288