Trapping of the Putative Cationic Intermediate in the Morin Rearrangement with Carbon Nucleophiles

Abstract

This paper presents reactions in which the putative cationic intermediate in the Morin rearrangement is trapped by aromatic carbon nucleophiles (indoles and furans). For example, reaction of sulfoxide 27 with trifluoroacetic acid in chloroform provides, among other products, indole 29 and indoline 30. The indoline was shown to be in equilibrium with the nine-membered ring bridged indole 31. Other examples of Morin rearrangement-trapping reactions are presented, and mechanisms for these transformations are proposed.

Phenyliodine(III) Diacetate/I2‐Mediated Domino Approach for Pyrrolo[1,4]Thiazines and 1,4‐Thiazines by a One‐Pot Morin Rearrangement of N,S‐Acetals

“…On the other hand, the first chemical examples leading to fused 1,4‐thiazines 11 were reported by Hart's group in 2001 [Scheme , Eq. (2)] . Depending on the R group, the ring expansion is promoted with trifluoroacetic anhydride (TFAA) or trifluoroactic acid (TFA)/CHCl 3 in 1/10 ratio starting from sulfoxides 10 [Scheme , Eq.…”

“…Regarding the mechanism, it is assumed now that the Morin reaction needs an oxidizing agent for the sulfoxidation and a base for the proton abstraction . Contrary to the above two examples which need two steps, only one example using benzothiazolylacetates 12 and m CPBA was reported.…”

“…(2)]. [18] Depending on the Rg roup, the ring expansion is promoted with trifluoroacetic anhydride (TFAA) or trifluoroactic acid( TFA)/CHCl 3 in 1/10 ratio starting from sulfoxides 10 [Scheme 1, Eq. (2)].…”

The spiroquinazoline family of alkaloids: a review

“…One failed approach to spiroquinazoline is described in Schemes 14-16. 40,41 The plan (Scheme 14) was to generate an N-acyliminium ion of type 85 by electrophile initiated ionization of an N,S-acetal of type 84. Scheme 14 depicts a methyl cation equivalent (iodomethane for example) as the S-activating group, but a number of alternatives were imagined.…”

Direct organocatalytic coupling of carboxylated piperazine-2,5-diones with indoles through conjugate addition of carbon nucleophiles to indolenine intermediates

“…17,18 This remarkable reaction involves coupling of the nucleophilic substrate with gramine in refluxing acetonitrile in the presence of trialkylphosphine. This reaction has received a number of applications, for example, in the synthesis of paraherquamide A19 and B,20,21 by Williams and coworkers as well as in the mechanistic study of the Morin rearrangement,22 although it uses toxic trialkylphosphine and generally gives product in moderate yields (40–70%). An interesting modification of this reaction has been reported by Hart and Magomedov, where treatment of substituted diketopiperazine with Li 2 CuCl 4 followed by the addition of gramine methosulfate gave coupling product in 54% yield.…”