*2.1. Synthesis of 5a–n*

The requisite spirooxindoles analogous were prepared by a multicomponent reaction (Scheme 1). The advantages of this efficient method were low-cost and readily available synthons for the synthesis of highly divergent compounds with high-importance applications. Fourteen analogues were prepared through the reactions of *bis*-benzylidine **1a–n,** which had been prepared according to our previous publication [9] with thioproline and 5,7-dibromoisatin, to afford the requisite target compounds. The chemical features of the requisite compounds were assigned based on HNMR, CNMR, IR, and CHN analysis.

**Scheme 1.** Synthesis of tetrahydro-1*H*-spiro[indoline-3,5'-pyrrolo [1,2-*c*]thiazol]-2-one **5a–n**.

According to Scheme 2 and based on our previous study [9], the reaction proceeds *via* one pot reaction, in which initially 5,7-dibromoisatin **2** reacted with thioproline **3** affording the azomethine ylide after the removal of carbon dioxide from the intermediate. Subsequently, the azomethine ylide reacted with the *bis*-benzylidine **1a–n** to provide the target compounds in a regioselective and diastereoselective manner. The reaction proceeded *via* path A regio-selectively to afford the regioisomer products **5a–n**, while the second regio-isomers **5a–n'** did not occur (path B). There are possible diastereoselective products that could be formed, but in this case only diastereoselective compounds **5a–n** occurred *via* the path C not D.

**Scheme 2.** Plausible reaction mechanism of the synthesized compounds.
