A Formal Synthesis of (−)-Perhydrohistrionicotoxin Using a Cross Metathesis–Hydrogenation Approach

The development of an efficient, high yielding six-step convergent synthesis of the semisynthetic alkaloid (−)-perhydrohistrionicotoxin is described. The key transformations include the cross metathesis of a Brønsted-acid masked primary homoallylic amine with a vinyl cyclohexenone and a regioselective palladium catalyzed hydrogenation. This sequence generated the advanced Winterfeldt spirocyclic precursor in 47% overall yield, with a longest linear sequence of five steps

Influence of Phosphoramidites in Copper-Catalyzed Conjugate Borylation Reaction

Copper­(I) has become the preferred metal to catalyze the β-boration of α,β-unsaturated carbonyl compounds, and now we demonstrate that easily accessible monodentate chiral ligands, such as phosphoramidites and phosphites, can be convenient alternative ligands to induce asymmetry in the enantioselective version of this reaction, particularly in the β-boration of α,β-unsaturated imines

Lutidine-Derived Ru-CNC Hydrogenation Pincer Catalysts with Versatile Coordination Properties

Lutidine-derived bis-N-heterocyclic carbene (NHC) ruthenium CNC–pincer complexes (Ru-CNC’s) were prepared. Depending on the synthetic procedure, normal (<b>1</b>, <b>2</b>) or mixed normal/abnormal NHC-complexes (<b>3</b>) are formed. In the presence of phosphazene base, Ru-CNC complexes activate nitriles to give ketimino compounds <b>4</b>–<b>6</b>. Nitrile adduct <b>4</b> shows reactivity toward strong bases to yield dearomatized complex <b>7</b>, which heterolytically activates H₂ to form the bis-hydrido complex <b>8</b>. Finally, these Ru-CNC’s are active in catalytic hydrogenation of CO₂ to formate salts, and unlike the phosphine-containing Ru-PNP counterpart, they also catalyze the selective hydrogenation of esters to alcohols

Bis-N-heterocyclic Carbene Aminopincer Ligands Enable High Activity in Ru-Catalyzed Ester Hydrogenation

Bis-N-heterocyclic carbene (NHC) aminopincer ligands were successfully applied for the first time in the catalytic hydrogenation of esters. We have isolated and characterized a well-defined catalyst precursor as a dimeric [Ru₂(L)₂Cl₃]­PF₆ complex and studied its reactivity and catalytic performance. Remarkable initial activities up to 283 000 h^–1 were achieved in the hydrogenation of ethyl hexanoate at only 12.5 ppm Ru loading. A wide range of aliphatic and aromatic esters can be converted with this catalyst to corresponding alcohols in near quantitative yields. The described synthetic protocol makes use of air-stable reagents available in multigram quantities, rendering the bis-NHC ligands an attractive alternative to the conventional phosphine-based systems