Potentionmetrische PH-Bestimmung

Ohne Zusammenfassung     

1,4-Diazaspiro[2.2]pentanes as a flexible platform for the synthesis of diamine-bearing stereotriads

Nitrogen-containing stereotriads occur in a number of biologically active compounds, but general and flexible methods to access these compounds are limited mainly to the manipulation of chiral olefins. An alternative approach is to employ a highly chemo-, regio-, and stereocontrolled allene oxidation that can install a new carbon-heteroatom bond at each of the three original allene carbons. In this paper, an intramolecular/intermolecular allene bis-aziridination is described that offers the potential to serve as a key step for the construction of stereotriads containing vicinal diaminated motifs. The resultant 1,4-diazaspiro[2.2]pentane (DASP) scaffolds contain two electronically differentiated aziridines that undergo highly regioselective ring openings at C1 with a variety of heteroatom nucleophiles to give chiral N,N-aminals. Alternatively, the same DASP intermediate can be induced to undergo a double ring-opening reaction at both C1 and C3 to yield vicinal diaminated products corresponding to formal ring opening at C3. The chirality of a propargyl alcohol is easily transferred to the DASP with good fidelity, providing a new paradigm for the construction of enantioenriched nitrogen-containing stereotriads.     

Modular functionalization of allenes to aminated stereotriads

Nitrogen-containing stereotriads, compounds with three adjacent stereodefined carbons, are commonly found in biologically important molecules. However, the preparation of molecules bearing these motifs can be challenging. Herein, we describe a modular oxidation protocol which converts a substituted allene to a triply functionalized amine of the form C-X/C-N/C-Y. The key step employs a Rh-catalyzed intramolecular conversion of the allene to a strained bicyclic methylene aziridine. This reactive intermediate is further elaborated to the target products, often in one reaction vessel and with effective transfer of the axial chirality of the allene to point chirality in the stereotriad.     

Arylation of halogenated pyrimidines via a Suzuki coupling reaction

The Suzuki coupling reaction has been used extensively for the synthesis of a wide variety of unsymmetrical biaryl compounds. We have extended this reaction to demonstrate the utility of preparing monophenyl-, diphenyl-, or triphenylpyrimidine depending on the reaction conditions. Further, it has been shown that chloropyrimidine substrates are preferable over iodo-, bromo-, or fluoropyrimidines.     

Total synthesis of (+)-tanikolide via oxidative lactonization

(+)-Tanikolide has been synthesized in eight linear steps with a 31% overall yield. The key step in the synthesis utilizes a recently developed tandem oxidative cleavage-lactonization of a precursor alkenol to deliver the lactone moiety.