A new mechanistic pathway of propargylic alcohol activation
by
gold(I) catalysis has been proposed toward the efficient synthesis
of N-protected pyrroles, 5,6-dihydropyridin-3(4H)-ones
from N-protected 5-aminopent-2-yn-1-ol, and 5-aminopent-2-yn-1-ol.
Control experiments support that the reaction proceeded via the neighboring
group participation of the oxygen atom of propargylic alcohol to form
an allene oxide intermediate where the nucleophilic heteroatom attacks
intramolecularly. Further, this methodology is successfully extrapolated
toward the atom-economic synthesis of hydroxyalkyl indoles and benzofurans.
The short reaction time of 30 s, low catalyst loading of 0.5 mol %,
high yield, variation in the substrate scope, and procedurally simple
open-flask reaction conditions make this methodology highly applied.
Synthesis of β-hydroxyenones and its application toward development of tetrahydro-4H-pyran-4-one in an atom-economic fashion is limited. This manuscript describes a ruthenium-catalyzed atom-economic coupling of pent-2yne-1,5-diols and Michael acceptors as an efficient route for the synthesis of βhydroxyenones with excellent yields and high regioselectivity. The β-hydroxyenones further undergo a 6-endo trig cyclization under acid-catalyzed conditions to deliver the tetrahydro-4H-pyran-4-ones with high diastereoselectivity. An intramolecular aldol condensation under mild basic conditions and palladium-catalyzed oxidative aromatization was developed for the synthesis of hexahydro-6H-isochromen-6-ones and isochromanols, respectively, from highly substituted tetrahydro-4H-pyran-4-ones with excellent yield and diastereoselectivity. Overall, this work demonstrates the synthetic potential toward the synthesis of oxacycles like tetrahydro-4H-pyran-4-ones, hexahydro-6H-isochromen-6-ones, and isochromanols via an atom-economic catalysis.
A photoredox‐catalyzed, efficient protocol for the direct insertion of a ‐SCN group onto spiro[5.5]trienone via a dearomative cascade cyclization of biaryl ynone with inexpensive NH4SCN has been developed, employing 4CzIPN as a potent photocatalyst under blue‐light irradiation without external oxidant. This scalable 6‐exo‐trig cyclization led to the cascade formation of C−C and C−S bonds and incorporate diverse thiocyanated spiro compounds with excellent yield (up to 92 %). Additionally, mechanistic investigations with fluorescence quenching, cyclic voltammetry, and radical scavenging are presented. Gram‐scale synthesis and further functionalization of thiocyanated compounds highlight the potential utility of this methodology.
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