Selenium-π-Acid Catalyzed Oxidative Functionalization of Alkynes: Facile Access to Ynones and Multisubstituted Oxazoles

Abstract

Unprecedented selenium-catalyzed propargylic oxidation of alkynes is disclosed. Various propargylphosphonates and 3-alkynoates were efficiently converted to valuable ynones via unusual C–C triple bond migration and deselenenylation at a vinyl carbon. By the strategies of tautomerization of enamine intermediate and SN2 displacement, similar conditions were effective for the oxidative difunctionalization of ynamides to afford multisubstituted oxazoles with high regioselectivity. Mechanistic studies revealed these detailed processes.

Preparation of Oxazole Acetals from N‐Propargylamides Enabled by Visible‐Light‐Promoted Selenium‐π‐Acid Catalysis

“…Organoselenium catalysts have been widely studied as electrophiles for the synthesis of various compounds [8,9,11] . As an important part in this field, selenium‐π‐acid catalyst arose widespread attention which is mainly through the interaction between selenenium and π bond [9] .…”

“…As an important part in this field, selenium‐π‐acid catalyst arose widespread attention which is mainly through the interaction between selenenium and π bond [9] . In this context, the production of selenium‐π‐acid often requires excess oxidants [10,11] . For instance, Zhao et al.…”

“…For instance, Zhao et al. reported a selenium‐π‐acid catalyzed cyclization of N ‐propargylamides into oxazole aldehydes with stoichiometric amount of Selectfluor [11] . Although N−F type oxidants have good compatibility for deselenylation of selenium species produced in the system, [12] excessive oxidants may lead to over‐oxidation and inactivation of diselenide.…”

A selenium-catalysed para-amination of phenols

“…Selenium-containing small molecules, such as ebselen and its analogues, have also exhibited important antioxidant activity as GPx mimics 12 – 15 . Organoselenium-catalysed reactions have been widely employed in a number of different reactions 16 – 18 , and substantial progress has been made by Breder 19 – 21 , Wirth 22 – 24 , Denmark 25 , 26 , Yeung 27 and Zhao 28 – 31 in recent years. Notably, selenium has emerged as appropriate alternatives to precious metals as catalysts for the construction of C–N bonds 32 – 34 .…”

Preparation and Utility of N-Alkynyl Azoles in Synthesis

“…In 2017, Li published a cobalt-catalyzed synthesis of 5-aminooxazoles via a [3 + 2] cycloaddition of N -(pivaloyloxy)amides with N -alkynyl amides/azoles (Scheme 66) [104]. The researchers were interested in developing a Co(III)-catalyzed synthesis of amino-substituted isoquinolones via carbon-hydrogen (C-H) activation and were surprised when they isolated 5-aminooxazole as the sole product.…”