Azides allylic carbocations

Pearson et al. (40) observed an unprecedented low-temperature [3 + 2] or [3 + 3] cycloaddition of azides with allylic carbocations, yielding triazolines or dihydro-triazolines (Scheme 9.40). When the hydroxy azide 182 was treated with SnC at —78 °C, a diastereomeric mixture of crystalline triazohnes 183 was obtained. A... 

Azides undergo low-temperature [3 -t- 3] and [3 -1- 2] cycloaddition reactions to allylic carbocations to give dihydrotriazines and triazolines, respectively. Dihydrotriazines (323) are produced from N-alkylindole derivatives and triazohnes (324) from A-benzenesulfonylindole derivatives (Scheme 99) <94JOC2682>. 

LPDE mediated allylic substitutions have been investigated widely. Substitution reaction of allylic alcohols with silyl ketene acetals, allyl silanes, indoles, methoxymethyl vinyl ether, trimethylsilyl azide, trimethylsilyl cyanide, and propar-gyl silanes proceeds with LPDE (Scheme 3.9) [32, 33]. An experiment with allylic alcohol (5,6) proved that these reaction proceeds via generation of allylic carbocation (Scheme 3.10). Also with a combination of LPDE and AcOH (1 mol%), more efficient allylic substitutions proceed (Scheme 3.11) [34]. 

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