Ketene-S,S-acetals as 1,3-dipolarophiles. Reactivity towards electron-deficient azides.
✍ Scribed by William O. Moss; Robert H. Bradbury; Neil J. Hales; Timothy Gallagher
- Publisher
- Elsevier Science
- Year
- 1988
- Tongue
- French
- Weight
- 248 KB
- Volume
- 29
- Category
- Article
- ISSN
- 0040-4039
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✦ Synopsis
The reactivity of a series of ketene-S,S-acetals (2a-e) towards p-toluenesulphonyl azide and ethoxycarbonyl azide is determined by the nature of the substituents on both the dipolarophile and the
13-dipole. With p-toluenesulphonyl azide rearrangement of the I,3-dithianyl ring is observed to give (4), but with ethoxycarbonyl azide a different pathway is followed leading to p-amino ketene-S,S-acetals (6), albeit in low yield.
Cycloaddition reactions between azides and alkenes have become a powerful tool in heterocyclic synthesis.'
The initial cycloadducts (A3-1,2,3+riazolines) may rapidly expel nitrogen or, with reactions involving electron-rich dipolarophiles such as ketene-O,O-or N,N-acetals (l,Y=O,NR"),may undergo aromatization with loss of-R"OH or R",NH to give a 1,2,3-triazole as shown be10w.~*~