Regioselective cyclization of α,ω-alkynoic acids catalysed by TpRu complexes: synthesis of endocyclic enol lactones [Tp = hydrotris(pyrazolyl)borate]

Abstract

The sigma-enynyl complex [TpRu(C(Ph)=C(Ph)C identical to CPh)(P-MeiPr2)] efficiently catalyses the regioselective cyclization of alpha,omega-alkynoic acids to yield endocyclic enol lactones having ring size up to 12 atoms.

Metal Vinylidenes and Allenylidenes in Catalysis: Applications in Anti‐Markovnikov Additions to Terminal Alkynes and Alkene Metathesis

“…[80] The enynyl ruthenium complex [Ru(Tp)(PhC=C(Ph)C CPh)(PMeiPr 2 )] is remarkably active in the production of unsaturated lactones by endocyclization of a,w-alkynoic acids (Scheme 9). [81] In this reaction the presence of the basic phosphine favors the alkyne to vinylidene tautomerism and allows the formation of macrocyclic enol lactones.…”

Osmium‐Catalyzed 7‐endo Heterocyclization of Aromatic Alkynols into Benzoxepines

“…[18,19] Then, the a-electrophilic [2a, 20] center of the vinylidene could be susceptible to intramolecular attack by the alcohol to give the 2-oxacycloalkylidene osmium intermediates IV, [21] which, in the presence of py would afford vinylic osmium species V. [22] A related sequence has been proposed for the formation of lactones from carboxylic acids that contain a triple bond in the presence of catalytic amounts of a TpRu complex (Tp = hydrotris(pyrazolyl)borate). [23] Finally, protonolysis of the heterocyclic ligand would liberate the 3-benzoxepine 2 and regenerate I.…”

Metal Vinylidenes as Catalytic Species in Organic Reactions

“…[26] Thus α,ω-alkynoic acids (38) may be converted to the corresponding enol lactones 39, in one case even forming a macrocycle, in good to excellent yield by heating in the presence of a ruthenium catalyst (Scheme 13). The exclusive formation of the endocyclic enol lactones is consistent with vinylidene formation, followed by intramolecular trapping by the tethered carboxylic acids.…”