title: From osmium hydrido vinylidene to osmacycles: the key role of osmabutadiene intermediates.
abstract: Osmium hydrido vinylidene 1 shows diverse cyclization reactivity with activated terminal alkynes. Treatment of 1 with HC≡CCOR' (R'=OEt and Me) gave osmafurans 3a and 3b via osmium alkenyl/vinylidenes 2a and 2b. In addition, 1 reacted with HC≡CCH(OH)C≡CH to yield osmabenzene 4, in which the alkynol acted as a C(5) fragment to cyclize with 1. Mechanistic analysis indicates that these reactions and the previous formal [3+3] cycloadditions between 1 and HC≡CCH(OH)R (R=Ph, Et, and vinyl) or HC≡CCH(OEt)(2) all go through similar osmabutadiene intermediates. Subsequently, the intermediates either took a "coordination and cyclization" process or a "carbon-carbon coupling" path to cyclization, depending on the coordination ability of substituents on the terminal alkenyl carbon atom.
authors.affiliation: State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, P. R. China.
authors.forename: Qianyi
authors.initials: Q
authors.lastname: Zhao
authors.forename: Xiao-Yu
authors.initials: XY
authors.lastname: Cao
authors.forename: Ting Bin
authors.initials: TB
authors.lastname: Wen
authors.forename: Haiping
authors.initials: H
authors.lastname: Xia