Temperature and para-substituent effects on the face selectivity of 1,3- dipolar cycloaddition reactions of benzonitrile oxides with 5-substituted adamantane-2-thiones, N-benzyladamantyl-2-imines, and 2-methyleneadamantanes

Tzong Liang Tsai, Wei Cheng Chen, Chin Hui Yu, W. J. Le Noble, Wen-Sheng Chung*

*Corresponding author for this work

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

The 1,3-dipolar cycloaddition reactions of para-substituted benzonitrile oxides (5-Y) with 5-fluoroadamantane-2-thione (2-F) and -2- methyleneadamantane (3-F) as well as with variously 5-substituted-N- benzyladamantyl-2-imines (4-X) were examined. They produce two geometrically isomeric Δ2-1,4,2-oxathiazolines (7-F,Y), Δ2-isoxazolines (8-F,Y), and Δ2-1,2,4-oxadiazolines (11-X,Y), respectively. The face selectivity in the latter reaction was found to be ~1:1 regardless of the variations in 5- substituent and the temperature. For the former two reactions, the para- substituent was varied from electron-withdrawing (Y = F, Cl, Br, CN, or NO2) to -releasing (Y = Me, or OMe). The face selectivity was measured in all cases. The differences Δp for the reactions of 2- and 3-F with 5-Y were obtained from linear Hammett plots; they are +0.12 and 0.0, respectively. These low values and information from previous studies imply a concerted one- step mechanism with very little charge distribution differences in the transition states. These effects of temperature on the Z/E product ratios provide us, for the first time, with activation parameter differences between the syn- and anti transition states; their values are discussed. The product bias resulting from the favored attack of nitrile oxide on the zu face is discussed in terms of transition state hyperconjugation based on the experimental results and AM1 calculations.

Original languageEnglish
Pages (from-to)1099-1107
Number of pages9
JournalJournal of Organic Chemistry
Volume64
Issue number4
DOIs
StatePublished - 19 Feb 1999

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