Alkynes as Electrophilic or Nucleophilic Allylmetal Precursors in Transition-Metal Catalysis

Catalytic nucleophilic 'umpoled' π-allyl reagents

After seminal Tsuji-Trost reactions (palladium catalyzed allylation of nucleophiles via π-allyl intermediates as electrophiles), the idea of reversal reactivity of π-allyl intermediates (i.e. π-allyl as nucleophiles) has been stated since the eighties. Thanks to different transition metal sources and the modification of their electronic environment through the use of additives and ligands, such 'reactivity switch' of π-allyl intermediates proved its powerfulness allowing high control in regio-, diastereo- and enantio-selectivities. These methodologies have thus emerged as efficient methods in the catalytic enantioselective allylation of carbonyl compounds and imines with a deep impact on natural product and/or drug elaboration. This tutorial review highlights the concept of 'umpoled' reactivity of π-allyl intermediates, relying on selected recent examples.

Copper-catalyzed, silver-mediated formal [3+2] cycloaddition of simple alkynes with β-ketoesters through propargylic C(sp3)–H functionalization

The propargylic C(sp³)–H functionalization strategy has been successfully employed in the copper-catalyzed [3+2] cycloaddition of simple alkynes with β-ketoesters. Under optimal conditions, the reaction proceeds smoothly to give a variety of highly functionalized furans in moderate to high yields.

Carbonyl anti-(α-Amino)allylation via Ruthenium Catalyzed Hydrogen Autotransfer: Use of an Acetylenic Pyrrole as an Allylmetal Pronucleophile

A single ruthenium complex catalyzes two discrete transformations resulting in the net conversion of an acetylenic pyrrole and alcohols to products of carbonyl anti-(α-amino)allylation. An initial catalytic process enables isomerization of an alkyne to a kinetically more reactive allene. A second catalytic process promotes alcohol-to-allene hydrogen transfer to form an aldehyde-allylruthenium pair that engages in regio- and diastereoselective carbonyl addition. A related reductive coupling of aldehydes mediated by 2-propanol also is described. The present catalytic processes represent rare examples of the use of alkynes as nucleophilic allylmetal precursors.

Accessing 1,3-Dienes via Palladium-Catalyzed Allylic Alkylation of Pronucleophiles with Skipped Enynes

An unprecedented palladium-catalyzed allylic alkylation of pronucleophiles with unactivated skipped enynes has been developed. This method provides a straightforward access to a wide array of 1,3-dienes without the need to preinstall leaving groups or employ extra oxidants. The reaction exhibited high atom economy, good functional group tolerance, excellent regioselectivities, and scalability. With D₂O as cosolvent, deuterium could be incorporated in high efficiency.