Base catalysed rearrangements involving ylide intermediates. Part 16. The preparation and thermal rearrangement of allylammonioamidates

Abstract

The ammonioamidates (7) and (11) undergo [1,2] rearrangement (R³= CH₂Ph) and competing [1,2] and [3,2] rearrangements (R³= allyl). The rates of the [1,2] and [3,2] rearrangements of the cinnamyl ammonioamidates (11a), (11b), (11d), and (11g) show similar dependence on the nature of the substituent X. The rate of the [1,3] rearrangement of the reaction products (14b), (14d), and (14g) is relatively insensitive to substituent effects, suggesting that the rates of ammonioamidate rearrangements are largely controlled by conjugation between the group X and the CO system. The [1,2] and [3,2] rearrangements of the cinnamylammonioamidate (11d) show moderate and similar dependence upon solvent polarity suggesting that the transition state for both reactions has considerable dipolar character. The apparent intramolecularity of the [1,2] and [3,2] rearrangements of the cinnamylammonioamidate (11e) as estimated by isotopic mixing methods is decreased by isotopic scrambling in the ylide due to radical recombination to give ylide (11l) in addition to products (13l) and (14l). If allowance is made for this effect the [3,2] rearrangement appears to be largely, or even entirely, intramolecular and the [1,2] rearrangement shows intermolecularity comparable with that found for the rearrangements of analogous ammonium ylides under similar reaction conditions.