No abstract

The ruthenium catalyst generated in situ from Ru3(CO)12 and tricyclohexylphosphine, PCy3, promotes the redox-neutral C-C coupling of aryl substituted α-hydroxy esters to isoprene and myrcene at the diene C4-position, resulting in direct carbinol C-H prenylation and geranylation, respectively. This process enables direct conversion of secondary to tertiary alcohols in the absence of stoichiometric byproducts or premetallated reagents, and is the first example of C4-regioselectivity in catalytic C-C couplings of 2-substituted dienes to carbonyl partners. Mechanistic studies corroborate a catalytic cycle involving diene-carbonyl oxidative coupling.

Carbonyl propargylation has been the topic of intensive investigation for over half a century. [1,2] An effective approach to enantioselective carbonyl propargylation involves the addition of chirally modified allenylmetal reagents, [3][4][5][6][7] including axially chiral derivatives. [5] Contributions include allenylboron reagents that are chirally modified at boron, as reported by Yamamoto, [3a] Corey, [3b] and Soderquist, [3c,d] allenylstannanes that are chirally modified at tin, as first reported by Mukaiyama, [4] as well as axially chiral allenylstannanes, allenylsilanes, allenylboron, and allenylzinc reagents that engage aldehydes in enantioselective propargylation, as described by Marshall, [5a,b,e,f] Hayashi, [5d] and Panek, [5c] respectively. Increasingly effective protocols for carbonyl propargylation, which involve stoichiometric chirality transfer, continue to be developed. [6,7] Enantioselective aldehyde propargylation using allenyltin [8] and allenylsilicon [9] reagents may be catalyzed by chiral Lewis acids or chiral Lewis bases, as first reported by Keck [8a] and Denmark, [8f] respectively. Copper catalysts promote enantioselective carbonyl propargylation by employing allenylboron and propargylboron reagents, as reported by Kanai and Shibasaki and Boehringer-Ingelheim Pharmaceuticals Inc. [10] More recently, Schaus, Antilla, and Reddy reported chiral H-bond donor and Brønsted acid catalyzed propargylations using allenylboron reagents. [11] Finally, catalytic enantioselective Nozaki-Hiyama coupling of propargyl halides delivers products of carbonyl propargylation. [12] Withstanding the Nozaki-Hiyama protocol, [12] methods available for enantioselective carbonyl propargylation have relied on stoichiometric allenylor propargylmetal reagents. Moreover, while carbonyl propargylations for the construction of non-methylated polyacetate subunits are common, catalytic diastereo-and enantioselective propargylations that convert achiral reactants to polypropionate substructures remain undeveloped. We envisioned an alternative strategy for carbonyl propargylation based on the "transfer hydrogenative coupling" [13] of 1,3-Angewandte Chemie

The ruthenium(0) catalyst generated from Ru3(CO)12 and tricyclohexylphosphine or BIPHEP promotes successive C-C coupling of dienes to vicinally dioxygenated hydrocarbons across the diol, hydroxyketone and dione oxidation levels to form products of [4+2] cycloaddition. A mechanism involving diene-carbonyl oxidative coupling followed by intramolecular carbonyl addition from the resulting allylruthenium intermediate is postulated.

(E)-1,2-Dichlorovinyl ethers and amides are easily accessible from trichloroethylene via nucleophilic addition across in situ synthesized dichloroacetylene. A one-pot, sequential Suzuki-Miyaura coupling/intramolecular direct arylation between dichlorovinyl ethers and organoboronic acids provides easy access to a variety of benzofurans in only two steps from inexpensive commercially available compounds. The method is extendable to the preparation of indoles from the analogous dichlorovinyl amides.