Why will Boc get cleaved under acidic conditions while Alloc does not? Can Alloc somehow be resonance stabilized? If so, how? Any help would be appreciated.

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    $\begingroup$ All else being equal, t-Bu carbocation is easier to form than allyl carbocation (see chemistry.stackexchange.com/a/87701/16683); so the easiest explanation may be "carbocation stability", although "stability" needs to be carefully defined here: let's say $\Delta E$ for the reaction $\ce{R2NCO2X + H+ -> R2NCO2H + X+}$, where X = allyl or t-Bu. (Of course, $\ce{R2NCO2H}$ will decompose to $\ce{R2NH + CO2}$, but the energetic contribution there is independent of X.) $\endgroup$ Jun 26, 2021 at 23:24
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    $\begingroup$ Your original assertion that Alloc will not get cleaved by acidic conditions is incorrect. If you look at the reactivity charts in Greene' s "Protective Groups in Organic Synthesis" the reactivity of Alloc is very similar to tBoc. It is merely that acid condition are not routinely used in the literature for Alloc removal $\endgroup$
    – Waylander
    Jun 27, 2021 at 10:18
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    $\begingroup$ @Waylander The "more acid-stable" was given as an explanation in an organic chemistry workbook which discussed the total synthesis of Minfiensine by Overman and colleagues (Overman 2005). Quote directly from the Overman paper: "Because of the propensity of the aminal fragment to open under acidic conditions, the tert-butoxycarbonyl (Boc) protecting group had to be exchanged for an allyloxycarbonyl (Alloc) group prior to transforming the epoxide to an allylic alcohol." Indeed, they did not deprotect Alloc with acid later in the synthesis, but with Pd-catalyzed Tsuji–Trost reaction $\endgroup$
    – user21398
    Jun 27, 2021 at 15:05
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    $\begingroup$ It would be worthwhile to include this context, including a link to the paper, in your original question by editing it. $\endgroup$ Jun 27, 2021 at 16:20
  • $\begingroup$ @orthocresol Will do when I have the time soon. $\endgroup$
    – user21398
    Jun 27, 2021 at 20:31


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