Ambiphilic Vinylcarbenoid Reactivity of (α-(Tributylstannyl)-π-allyl)palladium(II) Species

Abstract

The ambiphilic vinylcarbenoid reactivity of (α-(tributylstannyl)-π-allyl)palladium(II) species is demonstrated by the reaction of acetoxystannanes with Pd(dba)2, which promotes electrophilic metal−carbene reactions such as dimerization and cyclopropanation of strained alkenes. On the other hand, Pd(PPh3)4 and dppe revealed the nucleophilic nature of the dimetallic intermediates through sequential reactions of the carbon−metal bonds with dimethyl malonate.

Cyclopropanation of Strained Alkenes by Palladium‐Catalyzed Reaction of 3‐Trimethylsilyl‐ or 3‐Pinacolatoboryl‐1‐arylallyl Acetates

“…Recently, Fillion demonstrated the ambiphilic vinylcarbenoid nature of an α‐tributylstannyl‐π‐allylpalladium complex 7b. In light of these results, it is evident that the carbon atom between the palladium and the trimethysilyl group in Trost’s gem ‐dimetallic intermediate A has a Brønsted base character, and can therefore subsequently undergo protodesilylation to produce π‐allylpalladium intermediate C in the presence of nucleophiles such as β‐keto esters or β‐diesters that possess acidic protons.…”

Palladium‐Catalyzed Diastereoselective Synthesis of (Z)‐Conjugated Enynyl Homoallylic Alcohols

“…In particular, trimethylenemethane‐palladium (TMM−Pd) species have been shown to participate as three‐carbon components in [3+2] cycloadditions with electron‐deficient acceptors [2] . While TMM−Pd species can function as amphiphilic allylating agents, stannylated and silylated π‐allylpalladium species have been applied to the cyclopropanation of strained alkenes and dimerization of carbenes [3,4] . Recently, we demonstrated the advantages of borylated π‐allylpalladium species I in multiple C−C‐bond‐forming reactions (Scheme 1a).…”

“…[2] While TMMÀ Pd species can function as amphiphilic allylating agents, stannylated and silylated π-allylpalladium species have been applied to the cyclopropanation of strained alkenes and dimerization of carbenes. [3,4] Recently, we demonstrated the advantages of borylated π-allylpalladium species I in multiple CÀ C-bond-forming reactions (Scheme 1a). For instance, species I can afford (Z)-homoallylic alcohols with high diastereoselectivity via the allylation of aldehydes, followed by coupling of the resulting cisvinylpalladium species with organometallic reagents such as triorganoboranes, [5a] arylstannanes, [5b] and vinylstannanes [5c] (Scheme 1a, top).…”

Palladium‐Catalyzed Three‐Component Reaction of 3‐(Tri‐n‐ butylstannyl)allyl Acetates, Aldehydes, and Triorganoboranes: An Alternative to the Carbonyl Allylation Using α,γ‐Substituted Allylic Tin Reagents

“…(2)]. However, decomposition of ( R )‐ 1a was observed and 1,6‐diphenyl‐1,3,5‐hexatriene was instead produced in 29% yield by the dimerization of the palladium‐complexed 3‐phenyl‐2‐propenylcarbene 12,13…”

“…The palladium‐Xantphos complex reacts with 1 to initially form a π‐allylpalladium intermediate C 14. The oxygen atom of an acetoxy group in C coordinates intramolecularly to the tributyltin group, leading to σ‐allylpalladium intermediate C′ 12. Accordingly, the palladium atom in the σ‐allylpalladium instead of the tin atom in the tributyltin group functions as a Lewis acid to form a putative trans ‐decalin‐like cyclic transition state D .…”