A Ba/Pd Catalytic System Enables Dehydrative Cross-Coupling and Excellent E-Selective Wittig Reactions

Abstract

A Ba/Pd cooperative catalysis system was developed to enable the dehydrative cross-coupling of allylic alcohols with P-ylides to occur directly and promote a subsequent Wittig reaction in one pot. A variety of multisubstituted 1,4-dienes were isolated in good to excellent yields with broad P-ylides (stabilized by both ester and ketone carbonyl groups) and aldehyde (aliphatic and aromatic) substrates with excellent E selectivity.

Insights into Substrate Self-Assisted Activation of Allylic Alcohols Guiding to Mild Allylic Substitution of Tautomerizable Heteroarenes

“…Based on these control experiments and the literature reports, ,,, a possible reaction mechanism was depicted in Scheme . As to this novel extra activator-free Tsuji–Trost reaction of allylic alcohols with tautomerizable heteroarenes, two activation paths might be involved in the activation of allylic alcohols (Scheme ).…”

“…The reactive allylic halides and esters which are liable to undergo oxidative addition with a palladium catalyst traditionally served as precursors of π-allylic fragments . From the viewpoint of environmental issues and atom-/step-economy, much attention has recently been paid to the direct use of simple allylic alcohols as preferable alternates because this kind of transformation with allylic alcohols only gives water as a byproduct, and moreover, the common allylic partners in Tsuji–Trost reactions are generally prepared from the corresponding alcohols . However, owing to the poor leaving character of the hydroxy group, an extra activator such as As 2 O 3 , B 2 O 3 , BEt 3 , or Ti­(O-iPr) 4 is generally required to promote the smooth cleavage of the C–O bond in allylic alcohols .…”

Calcium-catalyzed dehydrative allylation of P-ylides and sequential Wittig reaction for streamlined access to versatile 1,4-dienes

“…Recently, the direct Wittig reaction of homoallylic P-ylides with aldehydes was considered one of the most promising approaches to obtain 1,4-dienes. [6][7][8][9][10][11][12] This strategy represents a straightforward and practical manner and can greatly expand the scope of accessible substrates. In pioneering the allylation of P-ylides for preparing semi-stabilized homoallylic P-ylides, highly active allylic agents, such as allylic carbonates 6 and Morita-Baylis-Hillman carbonates, 7 were recognized as suitable precursors.…”

“…Then, we developed a Pd/Ba dual-catalytic system, 12 which enabled the dehydrative allylation of P-ylides to occur smoothly, and various allylic alcohols and aldehydes were tolerated (Scheme 1a, right). The aforementioned investigations rely highly on transition metal catalysis, [10][11][12] while the strong coordination to the transition metal of the allylic P-ylide posed challenges for the sequential Wittig reaction. Therefore, the development of convenient methodologies under transition metal-free conditions is highly demanded.…”

“…9 By selecting palladium catalysis, allylic amines 10 and alcohols 11 were identified as powerful allylic reagents in Ma and Tian's investigation, although there is some limitation in terms of P-ylides and aldehydes (Scheme 1a, left). Then, we developed a Pd/Ba dual-catalytic system, 12 which enabled the dehydrative allylation of P-ylides to occur smoothly, and various allylic alcohols and aldehydes were tolerated (Scheme 1a, right). The aforementioned investigations rely highly on transition metal catalysis, 10–12 while the strong coordination to the transition metal of the allylic P-ylide posed challenges for the sequential Wittig reaction.…”