Experimental and DFT studies on competitive heterocyclic rearrangements. Part 2: a one-atom side-chain versus the classic three-atom side-chain (Boulton-Katritzky) ring rearrangement of 3-acylamino-1,2,4-oxadiazoles.
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Experimental and DFT studies on competitive heterocyclic rearrangements. Part 2: a one-atom side-chain versus the classic three-atom side-chain (Boulton-Katritzky) ring rearrangement of 3-acylamino-1,2,4-oxadiazoles. / Pace, Andrea; Pibiri, Ivana; Piccionello, Antonio Palumbo; Buscemi, Silvestre; Vivona, Nicolo; Barone, Giampaolo.
In: J ORG CHEM, Vol. 72, No. 20, 20, 2007, p. 7656-7666.Research output: SCORING: Contribution to journal › SCORING: Journal article › Research › peer-review
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TY - JOUR
T1 - Experimental and DFT studies on competitive heterocyclic rearrangements. Part 2: a one-atom side-chain versus the classic three-atom side-chain (Boulton-Katritzky) ring rearrangement of 3-acylamino-1,2,4-oxadiazoles.
AU - Pace, Andrea
AU - Pibiri, Ivana
AU - Piccionello, Antonio Palumbo
AU - Buscemi, Silvestre
AU - Vivona, Nicolo
AU - Barone, Giampaolo
PY - 2007
Y1 - 2007
N2 - The experimental investigation of the base-catalyzed rearrangements of 3-acylamino-1,2,4-oxadiazoles evidenced a new reaction pathway which competes with the well-known ring-degenerate Boulton-Katritzky rearrangement (BKR). The new reaction consists of a one-atom side-chain rearrangement that is base-activated, occurs at a higher temperature than the BKR, and irreversibly leads to the corresponding 2-acylamino-1,3,4-oxadiazoles. An extensive DFT study is reported to elucidate the proposed reaction mechanism and to compare the three possible inherent routes: (i) the reversible three-atom side-chain ring-degenerate BKR, (ii) the ring contraction-ring expansion route (RCRE), and (iii) the one-atom side-chain rearrangement. The results of the computational investigation point out that the latter route is kinetically preferred over the RCRE and can be considered as the ground-state analogue of a previously proposed C(3)-N(2) migration-nucleophilic attack-cyclization (MNAC) photochemically activated pathway. The MNAC consists of the formation of a diazirine intermediate, involving the exocyclic nitrogen, that eventually evolves into a carbodiimide intermediate (migration); the latter undergoes a single intramolecular nucleophilic attack-cyclization step leading to the final 2-acylamino-1,3,4-oxadiazole.
AB - The experimental investigation of the base-catalyzed rearrangements of 3-acylamino-1,2,4-oxadiazoles evidenced a new reaction pathway which competes with the well-known ring-degenerate Boulton-Katritzky rearrangement (BKR). The new reaction consists of a one-atom side-chain rearrangement that is base-activated, occurs at a higher temperature than the BKR, and irreversibly leads to the corresponding 2-acylamino-1,3,4-oxadiazoles. An extensive DFT study is reported to elucidate the proposed reaction mechanism and to compare the three possible inherent routes: (i) the reversible three-atom side-chain ring-degenerate BKR, (ii) the ring contraction-ring expansion route (RCRE), and (iii) the one-atom side-chain rearrangement. The results of the computational investigation point out that the latter route is kinetically preferred over the RCRE and can be considered as the ground-state analogue of a previously proposed C(3)-N(2) migration-nucleophilic attack-cyclization (MNAC) photochemically activated pathway. The MNAC consists of the formation of a diazirine intermediate, involving the exocyclic nitrogen, that eventually evolves into a carbodiimide intermediate (migration); the latter undergoes a single intramolecular nucleophilic attack-cyclization step leading to the final 2-acylamino-1,3,4-oxadiazole.
M3 - SCORING: Zeitschriftenaufsatz
VL - 72
SP - 7656
EP - 7666
JO - J ORG CHEM
JF - J ORG CHEM
SN - 0022-3263
IS - 20
M1 - 20
ER -
