Sugunan A, Aparna VM, Rajendar G. Phosphonium Ion-Tethered Secondary Amines for Chemospecific 5-
Enolexo Aldol Condensations of 6-Ketoaldehydes.
J Org Chem 2023. [PMID:
38014421 DOI:
10.1021/acs.joc.3c02285]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
A novel and highly selective 5-enolexo-exo-trig aldol condensation of 6-ketoaldehydes is presented using a proline-based alkylphosphonium ion catalyst. Bulky and oxophilic phosphonium ion plays a vital role in facilitating kinetic aldenamine formation and activating keto groups for aldol addition. This innovative approach exclusively targets five-membered carbo- and heterocyclic aldehydes, involving unusual aldehydes as donors and ketones as acceptors. Especially, enolizable aryl keto aldehydes and heteroatom-embedded ketoaldehydes exclusively produced cyclized products with our new catalyst, while other catalysts provided predominantly self-aldol or decomposed products. The scope and diversity of the method demonstrated by synthesizing different carboxaldehydes, including cyclopentene, indene, dihydrofuran, benzofuran, dihydropyrrole, indole, thiofuran, dihydrothiofuran, and benzothiofurans.
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