Metal-induced cyclization of functionalized alkynes represents one of the most general approaches to prepare organic heterocycles. AlthoughR u II centers are well-established to promote alkyne to vinylidener earrangements and many Ru II -mediated alkyne cyclizations have been rationalized to be the resultso fp ost-vinylidene transformations, recent discoveries indicate that Ru II centers can serve as electrophiles and induce alkyne cyclizationsw ithoutv inylidene intermediacy. In this Minireview,a no verview of the Ru II -induced cyclization of heteroatom-functionalized alkynes in the last decadei sp rovided, with an emphasis on the discoveries and validations of the unconventional "non-vinylidene-involving" pathways. Recent Progress of Ruthenium-Induced Cyclization of AlkynesResearcho nt he activation of heteroatom-functionalizeda lkynes by Ru II complexes for oxygen-and nitrogen-containing heterocycles of different ring sizes (5-to 8-membered) continues unabated. Most reported Ru complexes ares upported by Cp (Cp = cyclopentadienyl) or structurally analogous h 5 -ligands, amine-or mixed amine/phosphine-basedc helates. In general, the catalyst loadings are almost lower than 10 mol %a nd can be as low as 0.5 mol %. Although the cyclizations are mostly demonstrated with terminala lkynes, there are increasing number of successful reports on cyclizing internal alkynes.T he use of proton shuttles( internal or external bases which facilitate protont ransfer) has been found to be critical in many of these catalytic reactions. Noteworthy,s everal recent studies clearly indicatet hat the "vinylidene-involving" and "non-vinylidene-involving" pathwaysd epicted in Scheme 1are competing mechanisms. In this section, Ru-catalyzedc yclization of heteroatom-functionalized alkynes in the last decade is discussed in chronological order,e xcept in the cases of certain serial or outlying works. Catalytic Ru II -mediated cyclizations of N/O-functionalized alkynesthrough "vinylidene-involving" pathwaysThe successful isolations of Fe-, Ru-, and Os-oxacarbene complexesf rom the reactions between homopropargylic/bis-ho-Scheme1.(a) Established mechanisms for the formation of Ru-vinylidene species. (b) Electrophilic cyclizationso fheteroatom-functionalized alkynes induced by Ru.[a] Dr.Scheme8.Ru-catalyzed cycloisomerizations of alkynols into 5-, 6-and 7membered oxacycles developed by Jia and co-workers. [13,14] Scheme7.Ru-catalyzed cyclizationso fa niline-and phenol-tethered alkynes into indoles and benzofurans, respectively developed by Grotjahn and coworkers. [11,12] Scheme9.Ru-catalyzed cycloisomerizations of hydroxyl-and amine-substituteda lkynes into isochromenes, indolesa nd isoquinolinones developedby Blacquiereand co-workers. [15][16][17] Scheme10. Ru-catalyzed cycloisomerizations of alcohol-tethered alkynes developedb yWen and co-workers. [18] Chem.E ur.Scheme20. Isolation of, and proposed formation mechanism for 4a.The synthesis of 4b is also depictedf or reference [31].Scheme21. Isolation of, and proposed formation mechanism for...

Ruthenafuran and osmafuran monocationic complexes [Ru([14]aneS4)(C ∧ O)] + or [M(bpy) 2 (C ∧ O)] + (C ∧ O = anionic bidentate chelate [C(OR)CHC(Ph)O] − ; [14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane; M = Ru, Os; bpy = 2,2′-bipyridine) have been prepared from reactions between phenylynone HCC(CO)Ph and [Ru ([14]aneS4)Cl 2 ] or [M-(bpy) 2 Cl 2 ] in alcoholic solvents ROH. The formation of metal− vinylidene intermediate, followed by nucleophilic attack by RO − , and carbonyl group coordination to the metal center are believed to be the key steps in the formation of these metallafurans. The nature of the anionic C ∧ O ligand was investigated by electrochemical, spectroscopic, and theoretical means. ■ INTRODUCTIONActivation of alkynes for functional and novel organic products by transition-metal complexes is one of the most important topics in organometallic chemistry. 1 It is well documented that alkynes generally interact with d6-transition-metal centers through the formation of reactive yet sometimes isolable metal−vinylidene intermediates, which can further transform into other carbon-rich organometallic species including metal− acetylide, −acyl, −allenylidene, −alkoxycarbene, and −carbyne complexes, depending on the functionality of the alkynes and the reactants available in the reaction mixture. 2, 3 Our group has been scrutinizing the reactivity between a variety of organic substrates and structurally well-defined d6-transition-metal complexes, and the spectroscopic properties of the derived organometallic complexes. 4 As an extension of this research direction, we now present the reactivity of a specific type of alkyne, phenyl-ynone HCC(CO)Ph, toward [Ru([14]aneS4)Cl 2 ] and [M(bpy) 2 Cl 2 ] (M = Ru and Os; [14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane; bpy = 2,2′-bipyridine) in alcoholic solvents ROH. Our results reveal that the resultant products are metallafuran monocationic complexes [Ru([14]aneS4)(C ∧ O)] + and [M(bpy) 2 (C ∧ O)] + , where C ∧ O represents an anionic bidentate [C(−OR)CHC(−Ph) O] − chelate. It is worth mentioning that metallafuran and other members of metallacycles have received extensive attention in the field of organometallic and theoretical chemistry, 5,6 and the reactivity reported in this work may represent a general synthetic approach for different metallafurans. Moreover, the electronic properties of the ruthenafurans and osmafuran have been probed by electrochemical, spectroscopic, and theoretical studies. ■ RESULTS AND DISCUSSION Synthesis and Characterizations. Ruthenafuran and osmafuran monocationic complexes 1−3 have been prepared in high yield (50−80%) from reactions between phenyl-ynone HCC(CO)Ph and metal precursors [Ru([14]aneS4)Cl 2 ] or [M(bpy) 2 Cl 2 ] (M = Ru, Os) in alcoholic solvents (Scheme 1).These metallafuran complexes are air stable in both solution and solid forms. The alkoxy group attached to the C α is determined by the alcoholic solvent used (cf. synthesis of 1 and 1′). The carbenoid character for the M−C bonds is indicated by the low-field 13 C NMR ...

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The two families of Ru -chromene and -chromone complexes isolated in this work represent the first examples of metalated chromene and chromone complexes synthesized through transition-metal-mediated cyclization of phenol-tethered ynone. These unprecedented metalated heterocyclic compounds exhibit remarkable features, such as pH-switchable metal-carbon bonding interactions, photo-triggerable release of organic chromone upon visible-light irradiation, and superior antioxidative property to their organic analogue (1,4-benzopyrone). These findings not only offer mechanistic insights into metal-induced activation of functionalized alkynes, but also add a new dimension to rational design of antioxidants and photo-responsive drug delivery systems.