Domino Catalysis: Palladium‐Catalyzed Carbonylation of Allylic Alcohols to β,γ‐Unsaturated Esters

Abstract

Palladium-catalyzed carbonylations of organic (pseudo)halides are of broad interest for both academic and industrial research. [1] In the last two decades, the majority of the work in this area focused on the application of new ligand systems and the extension of the range of nucleophiles for the carbonylation of aryl and vinyl halides (or related pseudohalides). Consequently, the development of general catalytic protocols for more challenging substrates remains an important but challenging goal. Based on our continuous interest in transition-metal-catalyzed reactions with CO, [1b] recently we became attracted by carbonylation of allylic compounds, which represents a straightforward and economic method for the synthesis of versatile building blocks, b,g-unsaturated carbonyl compounds. [2] In spite of the tremendous progress in nucleophilic allylic substitution reactions, [3] carbonylation of allylic compounds has received much less attention. Most of the reported examples demand preinstalled leaving groups, such as chlorides, [4] carbonates, [5] acetates, [6] or phosphates. [6b,e, 7] Obviously, this creates inherent problems such as significant waste generation and requires less efficient multistep sequences. Moreover, side reactions were observed for carbonylation of allylic halides owing to the accumulation of hydrogen halides in this reaction. However, by adding base to quench the acid, direct reaction with allylic halides is possible. [5a] In general, the resulting b,g-unsaturated carbonyl compounds are highly susceptible to base-catalyzed isomerization, affording a,b-unsaturated carbonyl isomers. [4e] In the well-established carbonylation of allyl alkyl carbonates it is difficult to introduce various nucleophiles owing to the preferred reaction of the alkoxides from the substrates. Besides, allylic carbonates are usually prepared from allylic alcohols and toxic chloroformates. Thus, the overall process is also not really halide-free. Notably, carbonylation reactions of allylic acetates, which are commonly used as electrophiles in Pd-catalyzed allylic substitution reactions, are much less effective. For example, high CO pressure or halide additives are needed. This inefficiency is explained by the formation of p-allylpalladium acetates, which readily undergo reductive elimination to give the starting acetates rather than CO insertion. [8] An ideal way to streamline carbonylation of allylic compounds from an economic and environmental point of view is to use of allylic alcohols directly as substrates. Alcohols are more widely available and represent more environmentally benign reagents, generating water as the sole by-product. Advantageously, the whole synthetic route is shortened because most of the above-mentioned substrates are obtained from the corresponding alcohols. Unfortunately, the poor leaving ability of the hydroxy group, combined with the possible side reactions caused by the released water, have hindered the application of allylic alcohols in carbonylation reactions. [3d] As a result, only ...

Direct Synthesis of an α,ω‐Diester from 2,7‐Octadienol as Bulk Feedstock in Three Tandem Catalytic Steps

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“…[10] The most general methoda llowing the application of different allylic alcohols and different alcohols was recently establishedb yB eller and co-workers. [11] In contrast to the tandeme ther formation/ether carbonylation, the alkoxycarbonylation of olefins into esters has been investigated more extensively.…”

Regioselektive Pd‐katalysierte Methoxycarbonylierung von Alkenen unter Verwendung von Paraformaldehyd/Methanol als CO‐Surrogat

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