Evaluation of N‐hydroxymethylphthalimide in alkaline medium: Novel entry to the tricyclic [1,3]oxazepine core via an intramolecular π and O‐cationic cyclization

Abstract

Fused isoindolo[1,3]benzo(or thieno)oxazepines 8a,b and one of their positional isomers aromatic tricyclic N,O‐acetals 13b are reported to occur efficiently in a three‐step sequence from N‐hydroxy‐methylphthalimide (6). The key step of this methodology is the intramolecular arylation of an endocyclic and/or exocyclic N‐acyliminium cation. The mechanism leading to these species, in particular to a tricyclic lactam 13b, is discussed.

Intermolecular and Intramolecular α-Amidoalkylation Reactions Using Bismuth Triflate as the Catalyst

“…These products were formed by addition of a thiophenate ion, generated in situ by cleavage of the CH 2 −S linkage under Bi(OTf) 3 influence, to the not yet cleaved N -acyliminium cation. Our group has already observed similar results in sulfur 8c and oxygen series using TFA as an N -acyliminium promoter. Whatever the changes in the experimental conditions, neither the π-cationic cyclization nor the tandem thiocyclization/isomerization/π-cyclization cascade products were detected.…”

Anionic, in Situ Generation of Formaldehyde: A Very Useful and Versatile Tool in Synthesis

“…Favoring cleavage of X−CH 2 O - with concomitant release of formaldehyde would be effective only if the leaving group X - is more stable than the alcoolate (Scheme ). For this purpose, we focused our attention toward benzotriazolylmethanol Bt-CH 2 −OH 1 , a commercially available reagent developed by Katritzky's group, and N -hydroxymethyl phtalimide 2 . Both have comparable pKa values around 8.3 and were expected to exhibit similar reactivities.…”

Bi(OTf)3‐Catalysed Access to 2,3‐Substituted Isoindolinones and Tricyclic N,O‐Acetals by Trapping of Bis‐N‐Acyliminium Species in a Tandem Process

“…All characteristic data of cyclised compound 15a are identical to those published recently by Roy and co-workers during their application of a bimetallic Ir-Sn catalyst for tandem reaction sequence of heterocyclisation/isomerisation/π-cyclisation using 3-hydroxy-N-phenyoxymethylisoindolin-1-one. [21] This sequence was initially proposed by us [3] in reports dealing with sulfur, [8][9][10]22] oxygen [10,23] and selenium [10] -containing N-acyliminum precursors. o-Substituted phenols with Bn, OH and Br also undergo the desired chemistry to render cyclic N,O-acetals 15b-d in moderate to low yields of 43 %, 45 % and 27 %, respectively.…”