Rhodium‐Catalyzed Diastereoselective Cyclization of Allenyl‐Sulfonylcarbamates: A Stereodivergent Approach to 1,3‐Aminoalcohol Derivatives

A diastereoselective and stereodivergent rhodium‐catalyzed intramolecular coupling of sulfonylcarbamates with terminal allenes is described and it provides selective access to 1,3‐aminoalcohol derivatives, scaffolds found in bioactive compounds. The reaction is compatible with a large range of different functional groups, thus furnishing products with high diastereoselectivities and yields. Moreover, multigram scale reactions, as well as the application of suitable product transformations were demonstrated.     

Stereodivergent and Protecting‐Group‐Free Synthesis of the Helicascolide Family: A Rhodium‐Catalyzed Atom‐Economical Lactonization Strategy

Natural products of polyketide origin, in particular small‐sized lactones often possess a very broad range of impressive biological activities. An efficient way to demonstrate the concise access to six‐membered lactones was emphasized as part of a stereodivergent and protecting‐group‐free synthesis of all three representatives of the helicascolide family. This strategy features an atom‐economical and highly diastereoselective rhodium‐catalyzed “head‐to‐tail” lactonization by an intramolecular addition of ω‐allenyl‐substituted carboxylic acids to terminal allenes, including the selective construction of a new stereocenter in the newly formed core structures. The excellent selectivities with which the helicascolide precursors were obtained are remarkable, thus resulting in an expeditious and highly efficient natural product synthesis.     

Catalytic Enantioselective Assembly of Homoallylic Alcohols from Dienes,Aryldiazonium Salts,and Aldehydes

A highly selective multicomponent carbonyl allylation reaction of 1,3‐butadienes, aryldiazonium tetrafluoroborates, and aldehydes has been established under the combined catalysis of palladium acetate and chiral anion phase transfer to render the favorable assembly of chiral Z‐configured homoallylic alcohols in high yields and with excellent levels of enantioselectivity.     

Catalytic SN2′‐ and Enantioselective Allylic Substitution with a Diborylmethane Reagent and Application in Synthesis

A catalytic method for the site‐ and enantioselective addition of commercially available di‐B(pin)‐methane to allylic phosphates is introduced (pin=pinacolato). Transformations may be facilitated by an NHC–Cu complex (NHC=N‐heterocyclic carbene) and products obtained in 63–95 % yield, 88:12 to >98:2 S_N2′/S_N2 selectivity, and 85:15–99:1 enantiomeric ratio. The utility of the approach, entailing the involvement of different catalytic cross‐coupling processes, is highlighted by its application to the formal synthesis of the cytotoxic natural product rhopaloic acid A.     

Preparation and Reactivity of Acyclic Chiral Allylzinc Species by a Zinc‐Brook Rearrangement

The zinc‐Brook rearrangement of enantiomerically enriched α‐hydroxy allylsilane produces a chiral allylzinc intermediate, which reacts with retention of configuration in the presence of an electrophile. Two remarkable features of this transformation are the stereochemical outcome during the formation of the allylzinc species and the complete stereocontrol in the organized six‐membered transition state, which leads to an overall and complete transfer of chirality within the reaction sequence.     

Copper‐Catalyzed Borylcupration of Allenylsilanes

A highly regio‐ and stereoselective copper‐catalyzed borylcupration of 1,2‐allenylsilanes affords an unexpected regioreversed allylic boronate bearing an extra C?Si bond at the 3‐position, with a thermodynamically disfavored Z geometry. Such stereodefined allylic boronates containing an extra alkenyl silane moiety are very useful organodimetallic reagents for organic synthesis.     

[Cu(NHC)]‐Catalyzed C−H Allylation and Alkenylation of both Electron‐Deficient and Electron‐Rich (Hetero)arenes with Allyl Halides

New reactivity of a [Cu(NHC)] (NHC=N‐heterocyclic carbene) catalyst is disclosed for the efficient C?H allylation of polyfluoroarenes using allyl halides in benzene at room temperature. The same catalyst system also promotes an isomerization‐induced alkenylation of initially the generated allyl arenes when the reaction is run in tetrahydrofuran. Significantly, not only electron‐deficient but also electron‐rich (hetero)arenes undergo this double‐bond migration process, thus leading to alkenylated products. The present system features mild reaction conditions, broad scope with respect to the arene substrates and allyl halide reactants, good functional‐group tolerance, and high stereoselectivity.     

Synthesis and Utility of Dihydropyridine Boronic Esters

When activated by an acylating agent, pyridine boronic esters react with organometallic reagents to form a dihydropyridine boronic ester. This intermediate allows access to a number of valuable substituted pyridine, dihydropyridine, and piperidine products.     

Rhodium-Catalysed Selective C−H Allylation of 1H-Indazoles with Vinylethylene Carbonate: Easily Introducing Allylic Alcohol

An efficient rhodium(III)-catalysed C−H activation of 3-aryl-1-H-indazoles with easily available vinylethylene carbonate has been reported. A series of allyl alcohol substituted 3-aryl-1-H-indazoles were obtained with broad functional groups tolerance and favourable stereoselectivity. Notably, C−H and C−O bonds were selectively activated in “one pot” manner, releasing CO₂ as the sole by-product and avoiding external oxidant. This protocol provides a powerful approach for the post stage C−H allylation of indazole-based substrates.