ABSTRACT
A copper-mediated procedure for terminal alkynyl-propargyl coupling has been applied to "skipped" bis-terminal undecatetrayne and 1,4-bis(pseudo)halobut-2-ynes with the aim of preparing ring carbomers of representative strained and loose cycloalkanes, namely [N]pericyclynes. Two unprecedented, cyclic. "skipped" polyynes with CH2 vertices have been isolated as mixtures of diastereoisomers: an isomer 1b and a dimer 2a of [5]pericyclyne 1a. The isomer 1b is a cyclotetrayne with an exocyclic allene function resulting from a unique formal SN process. Its structure has been established by 1H/13C HMQC and HMBC two-dimensional NMR analysis. According to density functional theory calculations, it is about 6 kcalmol(-1) more stable than [5]pericyclyne (1a). Compound 1b can also be regarded as a C13-relaxed [4]pericyclyne, a long sought "skipped" C12 tetrayne. The dimer 2a is a C30 ring that results from a formal SN process. It is a stable ring carbomer of cyclodecane, that is, a [10]pericyclyne, with four CH2 vertices.
ABSTRACT
We just need to mix [Ru(CO)(3)Cl(2)(thf)] with methanolic NEt(4)OH-nature will do the rest: The unsaturated fragments thus generated spontaneously polymerize with production of CO(2) and H(2)O, which combine to give the carbonate ligands of the ruthena-crown species obtained (shown schematically). The carbonate groups, rarely seen in ruthenium carbonyl complexes, are responsible for the observed annulation, and hold consecutive Ru dimers together by acting as bridging and doubly chelating ligands.
