Palladium‐Catalyzed Three‐Component Reaction of Allenes, Aryl Iodides, and Diazo Compounds: Approach to 1,3‐Dienes

Abstract

Scheme 1. Transition-metal-catalyzed syntheses of 1,3-dienes.

Cooperative Iodide Pd(0)‐Catalysed Coupling of Alkoxyallenes and N‐Tosylhydrazones: A Selective Synthesis of Conjugated and Skipped Dienes

“…Our hypothesis was supported by a publication describing the synthesis of highly arylated butadienes by a three‐component coupling between aryl iodides, tosylhydrazones or diazo esters, and propadienyl arenes (Scheme ) . The role of N ‐tosylhydrazone in Pd 0 cross‐couplings is well established especially thanks to the pioneering work of Barluenga and Valdés and Wang . Examples of dienes obtained through Pd 0 ‐catalysed reactions of N ‐tosylhydrazones have been reported…”

“…[25] In our procedures, allenes were prepared by isomerisation of internal alkynes promoted by n-butyllithium, not compatible with electrophilic moieties. [27] The role of N-tosylhydrazone in Pd 0 cross-couplings is well established [28] especially thanks to the pioneering work of Barluenga and ValdØs [29] andW ang. [26] For this reason, we envisaged N-tosylhydrazones as ideal nucleophilic partners in aP d 0 -catalysed reaction,o wing to the requirementf or an additional carbon atom to assembly ab utadiene.O ur hypothesis was supported by ap ublicationd escribing the synthesis of highly arylated butadienes by athree-component coupling between aryl iodides, tosylhydrazones or diazo esters, and propadienyla renes (Scheme1).…”

“…In this context terminal allenes represent an appealing alternative, since mild isomerisation conditions are requiredf or propynole thers. [27,30] Examples of dienes obtainedt hrough Pd 0 -catalysed reactions of N-tosylhydrazones have been reported. [27] The role of N-tosylhydrazone in Pd 0 cross-couplings is well established [28] especially thanks to the pioneering work of Barluenga and ValdØs [29] andW ang.…”

“…[26] For this reason, we envisaged N-tosylhydrazones as ideal nucleophilic partners in aP d 0 -catalysed reaction,o wing to the requirementf or an additional carbon atom to assembly ab utadiene.O ur hypothesis was supported by ap ublicationd escribing the synthesis of highly arylated butadienes by athree-component coupling between aryl iodides, tosylhydrazones or diazo esters, and propadienyla renes (Scheme1). [27] The role of N-tosylhydrazone in Pd 0 cross-couplings is well established [28] especially thanks to the pioneering work of Barluenga and ValdØs [29] andW ang. [27,30] Examples of dienes obtainedt hrough Pd 0 -catalysed reactions of N-tosylhydrazones have been reported.…”

“…[27] The role of N-tosylhydrazone in Pd 0 cross-couplings is well established [28] especially thanks to the pioneering work of Barluenga and ValdØs [29] andW ang. [27,30] Examples of dienes obtainedt hrough Pd 0 -catalysed reactions of N-tosylhydrazones have been reported. [31] With the goal in mind of testing alkoxyallene reactivity in a three-component coupling with tosylhydrazones anda ryl halides, we set up ar eaction with iodobenzene, alkoxyallene 1a and benzophenonet osylhydrazone 2a.U nfortunately,o wing to the alkoxy group influence on the allene electronic properties, it was not possible to promote am ulticomponent process and the desired 1-alkoxy-1,3-diene 6a was afforded in low yield together with many side products virtually impossible to separate.N evertheless, one of these side productsw as easily isolateda nd characterised.…”