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First calculations of the structures of metal-free and complexed biaryl lactones and their confrrmation by X-ray crystaIlography, the search for the transition states of their heIimerization processes, and the spectroscopic determination of the heIimerization barriers of related cyclic ethers by DNMR are reported.
A practicable two-step procedure for the preparation of a series of lactone-type bridged biaryls 7 as favorable substrates for subsequent atropisomer-selective ring-opening reactions is described. Due to the efficiency of the coupling step, which tolerates even a telt·butyl group next to the biaryl axis and avoids problems of regioselectivity, a variety of differently substituted representatives is prepared. These cover a broad range of steric hindrance and thus molecular distortion. The structures are investigated mainly by NMR spectroscopy and X-ray diffraction, showing the lactones 7 to be helically distorted, depending on the size of the residues R.
The isolation and structure elucidation of rac-dioncophyllacine A from the leaves of Triphyophyllun peltatum, is described. Unlike all other naphthylisoquinoline alkaloids, this fully dehydrogenated representative has an additional methoxy group at C-4, the position of which is deduced from NOE results. Dioncophyllacine A has a 7,1' site of the biaryl axis, as in dioncophylline A. Its constitution is confirmed by an X-ray structure analysis, which shows that the crystalline form of this new alkaloid is racemic.
A convenient and new entry into the chemistry of highvalent pentamethylcyclopentadienyl halfsandwich complexes of molybdenum and tungsten is described. The reaction of Mo-(NtBu)\(_2\)Cl\(_2\) or W(NtBu)\(_2\)Cl\(_2\)(py)\(_2\) with Cp*Li (Cp* = \(\eta^5\)-C\(_5\)Me\(_5\)) provides a high-yield route to new complexes Cp*Mo-(NtBu)\(_2\)CI (la) and Cp*W(NtBu)\(_2\)Cl (1 b) which are converted into a variety of diimido, monoimido, and oxo derivatives. Treatment of 1 a, b with MeLi yields the highly volatile methyl derivatives Cp*Mo(NtBu)\(_2\)Me (2a) and Cp*W(NtBu)\(_2\)Me (2b), while protolysis of 1 a, b with an excess of HCI gas leads to selective cleavage of only one imido function with formation of Cp*Mo(NtBu)Cl\(_3\) (3a) and Cp*W(NtBu)Cl\(_3\) (3b). In contrast, protolysis of 1 a, b with aqueous HCI provides a high-yield route to the well-known organometallic oxides [Cp*MoO\(_2\)](μ-0) (4a) and [Cp*WO\(_2\)](\(\mu\)-0) (4b). These two key compounds are easily converted into the organomolybdate and organotungstate salts NBu\(_4\)[Cp*MoO\(_3\)] (5a) and NBu\(_4\)[Cp*WO\(_3\)] (Sb) by cleavage of the M - 0 - M bridge with NBu\(_4\)[OH]. The Xray structure of 3a is reported.