Kinetic Resolution of Chiral Cyclohex-2-enones by Rhodium(I)/binap-Catalyzed 1,2- and 1,4-Additions

The feasibility of kinetic resolutions of racemic monosubstituted cyclohex-2-enones by Rh/binap-catalyzed reactions was investigated. 1,2-Addition of AlMe₃ to the 5-substituted derivatives furnished allylic alcohols in the matched case, while the less reactive enantiomers were either left over or transformed into <i>trans</i>-3,5-disubstituted cyclohexanones in parallel or sequential 1,4-additions. Altogether, these represent regiodivergent reactions on racemic mixtures. In contrast, 1,4-addition of aryl groups led to inferior results since either catalyst or substrate control dominated

Total Synthesis of (<i>R</i>)‑Sarkomycin via Asymmetric Rhodium-Catalyzed Conjugate Addition

(<i>R</i>)-Sarkomycin was prepared using a five-step total synthesis. Key steps in the enantioselective construction of the targeted scaffold were a rhodium-catalyzed asymmetric conjugate alkenyl addition with subsequent silyl trapping and a Mukaiyama aldol reaction with aqueous formaldehyde. Protection of the hydroxy group as a THP acetal and oxidative cleavage of the C,C-double bond provided a stable direct precursor to the natural product. The final liberation was carried out under slightly acidic conditions in a microwave-assisted reaction, resulting in a high yield of the “deceptive” sarkomycin. This represents the shortest enantioselective synthesis of this rather unstable compound to date and the first to employ asymmetric catalysis to introduce the stereogenic center

Enantioselective Synthesis of 3,4-Disubstituted <i>cis</i>- and <i>trans</i>-1,2,5-Thiadiazolidine-1,1-dioxides as Precursors for Chiral 1,2-Diamines

Both, <i>cis</i>- and <i>trans</i>-3,4-disubstituted thiadiazolidines <b>5</b> and <b>6</b> can enantioselectively be obtained from thiadiazoles <b>2</b> which, in turn, are efficiently prepared from the respective 1,2-diketone by an improved protocol. An asymmetric ruthenium-catalyzed transfer hydrogenation followed by a diastereoselective hydride addition furnishes exclusively the <i>cis</i>-isomers <b>5</b> which, under acidic conditions, undergo a novel isomerization into the <i>trans</i>-isomers <b>6</b>. These cyclic sulfamides can be transformed into 1,2-diamines as well as 2,3-diamino acids

Enantioselective Synthesis of 3,4-Disubstituted <i>cis</i>- and <i>trans</i>-1,2,5-Thiadiazolidine-1,1-dioxides as Precursors for Chiral 1,2-Diamines

Both, <i>cis</i>- and <i>trans</i>-3,4-disubstituted thiadiazolidines <b>5</b> and <b>6</b> can enantioselectively be obtained from thiadiazoles <b>2</b> which, in turn, are efficiently prepared from the respective 1,2-diketone by an improved protocol. An asymmetric ruthenium-catalyzed transfer hydrogenation followed by a diastereoselective hydride addition furnishes exclusively the <i>cis</i>-isomers <b>5</b> which, under acidic conditions, undergo a novel isomerization into the <i>trans</i>-isomers <b>6</b>. These cyclic sulfamides can be transformed into 1,2-diamines as well as 2,3-diamino acids

Rhodium-Catalyzed Enantioselective Addition of Organoaluminum Reagents to <i>N</i>‑Tosyl Ketimines

Rhodium­(I)/Binap complexes catalyze highly enantioselective additions of methyl- and arylaluminum reagents to cyclic α,β-unsaturated <i>N</i>-tosyl ketimines. Depending on the solvent and substituents at the ring, the reaction occurs either in a 1,2-manner to deliver α-tertiary allylic amines or in a 1,4-manner to yield, after subsequent reduction, 3-substituted cycloalkyl amines. Well known in the case of the respective cycloalkenones, these first transformations of the aza-analogues enable the synthesis of amine structures of pharmaceutical and biochemical interest