Hydrogenative Cyclopropanation and Hydrogenative Metathesis

Abstract

The unusual geminal hydrogenation of a propargyl alcohol derivative with [CpXRuCl] as the catalyst entails formation of pianostool ruthenium carbenes in the first place; these reactive intermediates can be intercepted with tethered alkenes to give either cyclopropanes or cyclic olefins as the result of a formal metathesis event. The course of the reaction is critically dependent on the substitution pattern of the alkene trap.

Ammonium Acetate Catalyzed Formation of 1,5‐Benzodiazepines through [4+2+1] Cycloaddition Involving 5‐Hydroxymethylfurfural

“…After screening various diamines and alkynones/alkyl alkynoates for this three-component procedure, a series of substituted furfurals was investigated (Scheme 3). First, several 5-HMF-derived substrates, prepared from 5-HMF through known procedures [38][39][40][41] react smoothly under the optimized conditions affording the target products with yields of 71 % (4 p), 60 % (4 q), 65 % (4 r, as a (1 : 1) mixture of two diastereomers), and 71 % (4 s), respectively. Furfural and commercially available 5methylfurfural and 4,5-dimethyl furfural can also react well to give the desired products in the same range of yields (63 % to 70 %) (4 t-4 w).…”

“…The scope investigation was then extended to the alkynone reagent, using commercially available or easily prepared [34–37] alkynones or alkyl alkynoates (Scheme 2). Good yields of desired product were obtained when 1‐octyn‐3‐one or 1‐phenylprop‐2‐yn‐1‐one were used as reagents, giving the products 4 j and 4 k in 74 % and 67 % yields, respectively.…”

How to Break the Law: trans‐Hydroboration and gem‐Hydroboration of Alkynes

“…This striking reactivity mode has originally been observed in the context of ruthenium catalyzed alkyne hydrogenation: [57,62,63] indeed, trans ‐hydrogenation and gem ‐hydrogenation are intimately linked to each other. Since this discovery was made in 2015, gem ‐hydrogenation has evolved into a conceptually novel and versatile entry into pianostool ruthenium carbenes of type I (and true Grubbs‐type ruthenium carbene complexes as well); [64] as such, the reaction empowers a multitude of novel transformations including hydrogenative metathesis, [65,66] hydrogenative cyclopropanation, [65] hydrogenative rearrangements, [67,68] hydrogenative C−H functionalization, [69] and hydrogenative heterocycle syntheses [70] …”