Ruthenium‐Catalyzed Asymmetric Propargylic Substitution Reactions of Propargylic Alcohols with Acetone

Abstract

The table of contents entry for this paper contained an incorrect figure. The corrected entry is shown below. Enantioselective propargylic substitution reactions of propargylic alcohols with acetone catalyzed by a diruthenium complex give the propargylic alkylated products in good yields with up to 82 % ee (see scheme). A p-p interaction of phenyl rings between the ligand and allenylidene moieties is considered to play a crucial role in achieving such a high selectivity. Cp* = pentamethylcyclopentadiene.

Cooperative Catalysis: Enantioselective Propargylic Alkylation of Propargylic Alcohols with Enecarbamates Using Ruthenium/Phosphoramide Hybrid Catalysts

“…When other alkyl moieties, such as methyl and npropyl, were used in place of the ethyl group in 3 a, a similarly high enantioselectivity was observed in both cases (90 % ee and 96 % ee, respectively; entries 2 and 3). A variety of aryl groups can be used in place of the phenyl group in 3 to give the corresponding products with high diastereo-and enantioselectivities (entries [4][5][6][7][8]. Unfortunately, when the methyl group was used in place of aryl group in 3, only low diastereoand enantioselectivities were observed (entry 9).…”

“…The use of such hybrid catalysts may increase the reactivity and enantioselectivity of the reactions. As a result, the development of new types of cooperative transformations is anticipated by using the hybrid catalysts.As an extension of our study, [4,5] we have recently found the application of cooperative catalytic reaction systems, having two distinct catalysts, to enantioselective reactions of propargylic alcohols with carbon-centered nucleophiles, such as aldehydes, to give the corresponding propargylic alkylated products in high yields with an excellent enantioselectivity. [6] In these reaction systems, ruthenium complexes activate the propargylic alcohols to afford the corresponding allenylidene complexes, and organocatalysts, such as optically active amines, activate the carbon-centered nucleophiles to afford the corresponding enamines.…”

“…Typical results are shown in Table 2. A high enantioselectivity was observed when substituents such as methyl, methoxy, and chloro groups were introduced at the paraposition of the benzene ring of propargylic alcohols (entries [2][3][4]. The position of the methyl group on the benzene ring affected the enantioselectivity.…”

Cooperative Catalytic Reactions Using Organocatalysts and Transition‐Metal Catalysts: Enantioselective Propargylic Alkylation of Propargylic Alcohols with Aldehydes

“…Only two equivalents of 2 a relative to 1 a were used as a carbon-centered nucleophile; this is in sharp contrast to the previous reaction system for propargylic alkylation, wherein a large amount (i.e., as solvent) of the simple ketone was necessary to promote the propargylic alkylation. [5] The reaction proceeded more smoothly when three equivalents of 2 a relative to 1 a were used under the same reaction conditions. Other secondary amines such as (5S)-2,2,3-triScheme 1.…”

“…[3,4] We have previously found that the ruthenium-catalyzed propargylic alkylation of propargylic alcohols with acetone as a carbon-centered nucleophile gives the corresponding products with a high enantioselectivity (up to 82 % ee). [5] Unfortunately, the use of an excess amount of simple ketones such as acetone was necessary to promote the propargylic alkylation. We have envisaged that the enamines generated in situ from aldehydes and secondary amines can be applied as carbon-centered nucleophiles for the asymmetric propargylic alkylation.…”