Hydroacylation of 2-butyne from the alcohol or aldehyde oxidation level via ruthenium catalyzed C–C bond forming transfer hydrogenation

Abstract

Under the conditions of ruthenium catalyzed transfer hydrogenation, 2-butyne couples to alcohols 1a–1j to deliver α,β-unsaturated ketones 3a–3j in good to excellent isolated yields with complete E-stereoselectivity. Under identical conditions, aldehydes 2a–2j couple to 2-butyne to provide an identical set of α,β-unsaturated ketones 3a–3j in good to excellent isolated yields with complete E-stereoselectivity. Nonsymmetric alkyne 4a couples to alcohol 1d or aldehyde 2d in good yield to deliver enone 3k as a 5:1 mixture of regioisomers. Thus, intermolecular alkyne hydroacylation is achieved from the alcohol or aldehyde oxidation level. In earlier studies employing the same ruthenium catalyst under slightly different conditions, alkynes were coupled to carbonyl partners from the alcohol or aldehyde oxidation level to furnish allylic alcohols. Therefore, under the conditions of C-C bond forming transfer hydrogenation, all oxidation levels of substrate (alcohol or aldehyde) and product (allylic alcohol or α,β-unsaturated ketone) are accessible.

Ruthenium-Catalyzed Transfer Hydrogenation for C–C Bond Formation: Hydrohydroxyalkylation and Hydroaminoalkylation via Reactant Redox Pairs

“…60 These processes are catalyzed by (TFA) 2 Ru(CO)(PPh 3 ) 2 in the absence of added phosphine ligand. It is postulated that coordinative unsaturation, the presence of a π-acidic carbonyl ligand and the reducing environment provided by 2-propanol promote equilibration between ruthenium(II) and ruthenium(0) complexes.…”

Tin(II) Chloride Mediated Coupling Reactions between Alkynes and Aldehydes

“…Nevertheless, the coupling reactions between alkynes and Lewis acid activated aldehydes provide one example of the addition of carbon electrophiles to alkynes. Such coupling reactions have been carried out with SbF 5 ,4 GaCl 3 ,5 In(OTf) 3 ,5,6 Yb(OTf) 3 ,7 FeCl 3 ,8 or TMSOTf9 as the Lewis acid, and form a remarkable methodology for the production of ( E )‐α,β‐unsaturated ketones accompanied by skeletal transformation 10–13. We have studied the possible applications of the relatively weak Lewis acid, tin(II) chloride, which is insensitive to water and air, in organic synthetic reactions, and found that it catalyzes the propargylic substitution of propargylic alcohols with carbon and nitrogen nucleophiles in nitromethane;14 oxophilic tin(II) chloride cleaves the propargylic C–O bond leading to propargylic substitution.…”

Alkyne–Aldehyde Reductive CC Coupling through Ruthenium‐Catalyzed Transfer Hydrogenation: Direct Regio‐ and Stereoselective Carbonyl Vinylation to Form Trisubstituted Allylic Alcohols in the Absence of Premetallated Reagents

“…In previous studies on the coupling of 2‐butyne to alcohols and aldehydes under the conditions of ruthenium‐catalyzed CC bond‐forming transfer hydrogenation, it was found that dehydrogenation of the initially formed allylic alcohols could be induced to provide products of intermolecular alkyne hydroacylation from the alcohol or aldehyde oxidation level [Eq. (4)] 12b. These products of alkyne hydroacylation are not formed under the conditions used here.…”

“…Whereas previous studies focused primarily on the reductive coupling of 2‐butyne, a symmetrical alkyne,12a,b it was found that the catalyst prepared from [Ru(TFA) 2 (CO)(PPh 3 ) 2 ] (TFA=O 2 CCF 3 ) and Bu 4 NI enables the regioselective reductive coupling of nonsymmetric alkynes and paraformaldehyde 12c. Based on this result, a survey of higher aldehydes was undertaken.…”