Substrate-Controlled Regioselectivity Switchable [3 + 2] Annulations To Access Spirooxindole Skeletons

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Stereoselective Synthesis

Background:

• Spirooxindole scaffolds are prevalent in natural products and pharmaceuticals.
• Efficient synthesis of complex spirooxindoles with multiple stereocenters remains a challenge.

Purpose of the Study:

• To develop a novel additive-free [3 + 2] annulation strategy.
• To synthesize functional and structurally complex 3,3'-pyrrolidinyl-spirooxindole derivatives.
• To investigate the regioselectivity of the annulation reaction.

Main Methods:

• Utilized isatins and amino acids (proline, thioproline, piperidine acid) with 2-styrylbenzoxazoles.
• Employed a [3 + 2] annulation reaction under additive-free conditions.
• Analyzed product structures and stereochemistry using analytical techniques.

Main Results:

• Achieved high yields (up to 95%) and excellent diastereoselectivities (up to >25:1 dr).
• Generated spirooxindole derivatives containing four contiguous and two quaternary stereogenic centers.
• Demonstrated switchable regioselectivity (α- vs. γ-) based on the amino acid substrate.

Conclusions:

• The developed method provides efficient access to complex spirooxindoles.
• The reaction's regioselectivity can be controlled by substrate selection.
• This work offers a valuable synthetic route for stereochemically rich spirooxindole compounds.