The
combination of the metal-catalyzed cycloisomerization of alkynes
containing a tethered nucleophile as substituent in aqueous media
(followed by the spontaneous hydrolysis, hydroalkoxylation, or aminolysis
of the transiently formed five-membered heterocycles) with the subsequent
enantioselective ketone bioreduction (mediated by KREDs) has been
achieved. The overall transformations, which formally involve a three-step
one-pot reaction, provide a variety of enantiopure valuable molecules
(e.g., 1,4-diols, lactones, and γ-hydroxy-carbonyl compounds
(carboxylic acids, esters, and amides)) with high conversions and
enantioselectivities and under mild reaction conditions, disclosing
the concept of integrated metal-catalyzed cycloisomerizations of alkynes
and enzymatic catalysis in water.
New iminophosphorane-phosphine Au complexes [AuCl(κ -P-Ph PCH P{=NP(=S)(OR) }Ph )] (3 a,b) and [Au Cl (μ -P,S-Ph PCH P{=NP(=S)(OR) }Ph )] (4 a,b) proved to be general, very efficient, and recyclable (up to four consecutive runs) catalysts for the cycloisomerization of alkynyl amides in water or choline chloride-based eutectic mixtures as green solvents. Remarkably, this cycloisomerization reaction took place under mild conditions (low catalyst loading, at room temperature, and in the absence of cocatalysts or protecting atmosphere) to give the corresponding alkylidene lactams by employing an efficient and sustainable methodology.
The subsequent double-bond isomerization in the synthesis of dibenzocycloheptenes and their heteroaromatic analogues was investigated. In the case of biphenyls, a basic additive completely prevented an isomerization to the thermodynamic product. With electron-rich intramolecular heteroaromatic nucleophiles, the isomerization was still observed, but the kinetic product can be obtained by careful control of the reaction times in most cases. Mechanistic studies demonstrated that a slow isomerization is also possible with the gold catalyst at elevated temperatures, but much faster isomerization rates were observed with acidic additives. An observed initiation period for the gold-catalyzed isomerization indicates that not the homogenous catalyst, but a decomposition product of it may be the catalytically active species.
The
synthesis of four different monofunctional vinyl cyclopropane
(VCP) derivatives and their polymerization behavior is presented.
The different VCPs have different capabilities to form hydrogen bonds
in their side chain. A preorganization due to these hydrogen bonds
should lead to a fast polymerization. Kinetic studies, hydrogen-bond
strength, and theoretical calculations were used to correlate the
degree of conversion and the amount of preorganization. While VCPs
capable of hydrogen bonding did not show a huge difference, a general
effect of hydrogen bonds on polymerization behavior could be observed.
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