3-(E)-But-2-enoxy-1,2-benzisothiazole 1,1-Dioxide: Unusual C-O-C Ether Bond Lengths and Reactivity

Ethers such as the title compound, C₁₁H₁₁NO₃S, (1), rearrange thermally to give N-allyl isomers, (2), in high yield. The X-ray structure determination of the title ether shows a central C-O-C linkage which has one very short (notional) C-O single bond and one exceptionally long single C-O bond. The thermal migration of allyl from the O to the N atom involves the breaking of one of the ether bonds in (1) and a shortening of the other as it becomes a formal carbonyl group in the product (2). The rearrangement is thus considerably assisted by the ground-state structure of the starting ether, in which the bond to be broken is already stretched and the one that is to form a carbonyl group is already a substantial partial double bond.

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