Platinum(II)‐Catalyzed Reaction of γ,δ‐Ynones with Alkenes for the Construction of 8‐Oxabicyclo[3.2.1]octane Skeletons: Generation of Platinum‐Containing Carbonyl Ylides from Acyclic Precursors

Abstract

Transition-metal-containing zwitterionic intermediates generated through the electrophilic activation of alkynes toward nucleophilic attack by a carbonyl oxygen atom or imino nitrogen atom can be used in addition reactions with nucleophiles or cycloaddition reactions with alkenes or alkynes to prepare synthetically useful heterocyclic compounds. [1][2][3][4][5] However, in almost all cases, it is necessary to employ rigid aromatic substrates for the effective generation of the zwitterionic species. Herein, we report a catalytic method for the generation of nonconjugated platinum ( [6] was found to be very effective. Thus, the treatment of 1 a with platinum(II) chloride (10 mol %) in the presence of n-butyl vinyl ether at room temperature gave the 8-oxabicyclo[3.2.1]octane derivative 2 a in 78 % yield as a single diastereoisomer with the butoxy substituent in an exo orientation.We propose the following mechanism for the formation of 2 a: The electrophilic activation of the alkyne moiety in 1 a by platinum(II) chloride induces the attack of the carbonyl oxygen atom onto the alkyne in a 6-endo manner to generate the platinum-containing carbonyl ylide 3 a, which then undergoes a [3+2] cycloaddition reaction with n-butyl vinyl ether to give the nonstabilized carbene complex 4 a. Finally, a 1,2-hydrogen-atom shift to the carbene carbon atom gives the product 2 a with regeneration of the catalyst (Scheme 1).

Total Synthesis of (±)‐Englerin A Using An Intermolecular [3+2] Cycloaddition Reaction of Platinum‐Containing Carbonyl Ylide

“…According to the above synthetic plan, we first examined the construction of the oxygen‐bridged seven‐membered ring compound 6 . Generation and [3+2] cycloaddition reaction of the platinum‐containing carbonyl ylide proceeded efficiently by treatment of a mixture of γ,δ‐ynone 5 , and benzyl vinyl ether with catalytic amounts of PtCl 2 [P( m ‐tolyl) 3 ] and AgSbF 6 at room temperature to provide the desired cycloadduct 6 , which has the C15‐methyl and C9‐oxygen functionalities of 1 , in 90 % yield as a single diastereomer. Relative configuration of 6 was confirmed by observation of an NOE between the C9‐methine proton and the C1‐olefinic proton as shown in Scheme .…”

Recent developments in gold-catalyzed cycloaddition reactions

“…In particular, important developments were recently achieved with platinum catalysts [36–37], including the first enantioselective examples of these type of cycloadditions promoted by a chiral cationic platinum–diphosphine catalyst [38]. …”

Carbo- and heterocyclisation of oxygen- and nitrogen-containing electrophiles by platinum, gold, silver and copper species

“…13 The R 2 -substituent of g,d-ynones is crucial for the chemoselectivity as illustrated in Scheme 15. 13 The R 2 -substituent of g,d-ynones is crucial for the chemoselectivity as illustrated in Scheme 15.…”