Concise approach to pyrrolizino[1,2-b]indoles from indole-derived donor–acceptor cyclopropanes

Abstract

A direct approach to previously unexplored pyrrolizidino[1,2-b]indole system from indole-derived donor–acceptor cyclopropanes based on a sequence of three synthetic steps was developed.

4‐(Dimethylamino)Pyridinium Azide in Protic Ionic Liquid Media as a Stable Equivalent of Hydrazoic Acid

“…Next, we applied the reaction conditions optimized for the one ‐ pot transformation of 1 a to 3 a (Table 3, entry 9) for the synthesis of a series of 4‐azidobutyrates 3 (Scheme 4). Although the yields of the designed transformation were moderate and lower than those described earlier, [13,14d,f] these conditions granted a tremendous reaction rate increase. Thus, treating D‐A cyclopropane 1 a either at 100 °C for 7 h or at 120 °C for 2 h independently furnished the desired azide 3 a , while the conventional method required around 20 h on average.…”

3-(2-Azidoethyl)oxindoles: Advanced Building Blocks for One-Pot Assembly of Spiro[pyrrolidine-3,3′-oxindoles]

“…Synthesis of intermediate cyclopropanes 2 was performed through sequential Knoevenagel and Corey-Chaykovsky reactions according to the literature procedures. , Cyclopropanes 2a – i were obtained in good yields as diastereomeric mixtures. In order to carry out transformation of cyclopropanes 2 into azides 3 , we have modified the reaction conditions, previously reported by us for the nucleophilic ring opening of donor–acceptor cyclopropanes with the azide ion . To achieve complete 2 -to- 3 conversion, this process was thermally activated in a microwave reactor.…”

“…Recently, we have reported original access to pyrrolidine derivatives via a cascade of Staudinger/ aza -Wittig/Mannich reactions of carbonyl compounds with readily available organic azides, wherein the 1,3-relationship between the azido group and an activated CH-fragment provided desired reactivity (Scheme B). In this context, our further efforts were directed toward the development of a new approach to spiro­[pyrrolidine-3,3′-oxindoles] based on our original strategy for pyrrolidine assembly.…”

Ring Opening of Donor–Acceptor Cyclopropanes with N-Nucleo­philes

“…[165][166][167] The method for the synthesis of 213 relied upon nucleophilic ring opening of DA cyclopropanes 212 activated with aryl-, hetaryl-, and alkenyl-substituents as the EDG (R) and ester, acyl, nitro, and cyano groups as EWG with the azide ion (Scheme 120). 165 The experimental data showed that the reaction proceeded via an S N 2-like mechanism with reversal of configuration at the electrophilic center of cyclopropane 212.…”