Allenes and Dienes as Chiral Allylmetal Pronucleophiles in Catalytic Enantioselective C=X Addition: Historical Perspective and State‐of‐The‐Art Survey

Abstract

The use of allenes and 1,3-dienes as chiral allylmetal pronucleophiles in intermolecular catalytic enantioselective reductive additions to aldehydes, ketones, imines, carbon dioxide and other C=X electrophiles is exhaustively catalogued together with redox-neutral hydrogen auto-transfer processes. Coverage is limited to processes that result in both CÀ H and CÀ C bond formation. The use of alkynes as latent allylmetal pronucleophiles and multicomponent C=X allylations involving allenes and dienes is not covered. As illustrated in this review, the ability of allenes and 1,3-dienes to serve as tractable non-metallic pronucleophiles has evoked many useful transformations that have no counterpart in traditional allylmetal chemistry.

Understanding Halide Counterion Effects in Enantioselective Ruthenium-Catalyzed Carbonyl (α-Aryl)allylation: Alkynes as Latent Allenes and Trifluoroethanol-Enhanced Turnover in The Conversion of Ethanol to Higher Alcohols via Hydrogen Auto-transfer

“…Here, by understanding halide counterion effects , and exploiting trifluoroethanol (TFE)-enhanced turnover, we report an improved catalytic system for alkyne−alcohol C−C coupling, as illustrated by the regio- and enantioselective conversion of ethanol (the most abundant renewable small-molecule carbon source) to enantiomerically enriched homoallylic alcohols. Specifically, using a ruthenium catalyst modified by JOSIPHOS in the presence of TFE, diverse 1-aryl-1-propynes react with ethanol to form branched secondary homoallylic alcohols through a tandem catalytic cycle in which alkyne-to-allene redox isomerization is followed by allene−​aldehyde reductive coupling via hydrogen auto-transfer. − As corroborated by DFT calculations and crystallographic characterization of a series of halide-bound complexes, RuX­(CO)­(η 3 -C 3 H 5 )­(JOSIPHOS), where X = Cl, Br, or I, there exists a halide-dependent diastereomeric preference that defines metal-centered stereogenicity and, therefrom, the absolute stereochemical course of C−C coupling. Whereas the chloride- and bromide-bound catalysts exist as stereoisomeric mixtures, the iodide-bound catalyst exists as a single stereoisomer, enforcing superior levels of enantioselectivity.…”

Total Synthesis of the Acetyl CoA Carboxylase Inhibitor Soraphen A: Asymmetric Tsuji Reduction Enables Successive Olefin Metathesis

“…The synthesis of fragment B began with conversion of prenyl alcohol 5 to prenyl methyl carbonate (not shown), which was subjected to Riley-type oxidation to provide enal 6 . syn -Diastereo- and enantio­selective crotylation of enal 6 was achieved via 2-propanol-mediated reductive coupling with silyl-substituted diene 7 using a ruthenium catalyst modified by ( R )-SEGPHOS. , Desilylation of vinyl­silane 8 could be accomplished in situ or as a separate manipulation in roughly equivalent overall yield.…”

Acyclic Quaternary Carbon Stereocenters through Transition-Metal-Catalyzed Enantioselective Functionalization of Unsaturated Hydrocarbons

“…The controlled catalytic elaboration of dienes is thus of great synthetic importance. 23 On the other hand, methanol is produced in large volume each year (>30 × 10 6 tons/year). The direct conversion of methanol to higher alcohols is particularly attractive.…”