Synthesis and chemistry of chiral vinylrhenium complexes (.eta.-C5H5)Re(NO)(PPh3)(CH:CHR'). Stereoselective reactions with electrophiles and a spontaneous alkylidene to olefin rearrangement

Abstract

1,2-disubstituted and 1,2,3-trisubstituted aromatic hydrocarbons.Acknowledgment. This research was supported in part by a grant from the National Cancer Institute (CA 13963). Mass spectra were obtained from facilities provided under grants from the National Institutes of Health (CA 11388 and GM 16864) and NMR spectra from the University of Illinois Midwest NSF Regional NMR Facility (CHE 79-16100). We thank Professor Peter Beak for helpful discussions.(19) Traditional lithiation procedures must employ lithiating agents basic enough to convert the carbon acid largely to its conjugate base. The in situ trapping procedure can be useful with weaker bases if the deprotonation, to produce a small concentration of trappable aryllithium, is sufficiently rapid to make this process competitive in rate with reaction of the hindered base with the in situ electrophile.

Efficient endo Cycloisomerization of Terminal Alkynols Catalyzed by a New Ruthenium Complex with 8‐(Diphenylphosphino)quinoline Ligand and Mechanistic Investigation

“…nature of the C a and C b atoms of the vinylidene ligand,r espectively,i ntramoleculara ddition of the OÀHg roup to the C=C double bond of the vinylidene ligand could give the sevenmembered ruthenium oxacyclocarbene intermediate 12, [25] which then undergoes deprotonation to afford the vinyl complex C.F inally,p rotonation of the metal-carbon bond in C would give the organic compound 5a and regenerate A.T he conversion of metal-carbene to metal-vinyl is present in many catalytic transformations, andi ti sp articularly favored when the carbeneh as aC b ÀHb ond. [28,29] In this case, the C b proton of the oxacyclocarbene intermediate 12 is fairly acidic owing to the cationic nature of the complex.T hus, it should undergo deprotonation to afford C with the aid of the basic media present in the solution (probably this couldb et race amounts of water,t he hydroxy group of substrate 4a,o rt he ether functionality of product 5a).…”

Preparation and Reactivity of Hydridorhenium Complexes with Polypyridine and Phosphonite Ligands

“…Vinyl complexes of rhenium are rare21 and in some cases have been proposed only as intermediates 22. Our reaction of dihydrido compound 2a with a terminal alkyne provides new examples of this class of derivatives.…”

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

“…[18] Removal of the hydride as a proton by pyridine followed by re-protonation at the C b atom would afford the osmium-vinylidenes III. [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.…”