We have established that a cationic rhodium(I)-dppf complex catalyzes isomerizations of allyl propargyl ethers to allenic aldehydes in good yields from room temperature to 40 degrees C. On the other hand, carbonyl migration reactions from allenic aldehydes further proceed to give dienals in good yields at 80 degrees C.

The olefin isomerization/enantioselective intramolecular Alder-ene reaction cascade was achieved by using a cationic rhodium(I)/(R)-BINAP complex as a catalyst. A variety of substituted dihydrobenzofurans and dihydronaphthofurans were obtained from phenol- or naphthol-linked 1,7-enynes, respectively, with good yields and ee values.

Scheme 1. Previously reported olefin isomerization/propargyl Claisen rearrangement/carbonyl migration cascade of an enyne.Scheme 2. Design of the rhodium-catalyzed cascade reaction of dienyne 1.

Fünf in einem: Durch Rhodium(I)‐Binap‐Komplexe katalysierte Kaskadenreaktionen von Dieninen führen zur Bildung von 1,2‐Dihydronaphthalinen, Naphthalinen und 1,4‐Dihydronaphthalinen. Diese Kaskadenreaktionen umfassen bis zu fünf grundsätzlich verschiedene chemische Umwandlungen, einschließlich der katalytischen enantioselektiven Carboformylierung von Alkenen mit Aldehyden oder der Cycloisomerisierung von Enallenen.

A cationic rhodium(I)/1,1'-bis(diphenylphosphino)ferrocene (dppf) complex catalyzes isomerization of allyl propargyl ethers to allenic aldehydes in good yields at room temperature 40 °C. At 80 °C, carbonyl migration from allenic aldehydes proceeds further to give dienals in good yields. The cationic rhodium(I)/dppf complex acts as a dual catalyst for activation of σand π-bonds in these isomerization reactions.Cationic Rh(I) complex-catalyzed cascade reactions 1457Consistent with this pathway, enol ether 5d and allenic aldehyde 2d were observed by 1 H NMR at room temperature for 1 h. After 17 h, allenic aldehyde 2d was observed as a sole product (eq. 8). Furthermore, allenic aldehyde 2d and dienal 3d were observed by 1 H NMR at 80 °C for 1 h. After 16 h, dienal 3d was observed as a sole product (eq. 9).Four additional experiments further provide useful mechanistic information. Electrophilic PdCl 2 , which is known to be a very effective catalyst for isomerization of allyl ethers to enol ethers through electrophilic double-bond activation [15], did not catalyze isomerization of 1a to 5a, which suggests that the electrophilic double-bond activation by the cationic rhodium(I) complex might not be involved in this olefin isomerization (eq. 10). The thermal propargyl Claisen rearrangement of 5d to 2d did not proceed (eq. 11), while chiral induction was observed in the reaction of 1h to 4h by using a chiral rhodium(I) complex (eq. 12). These results clearly indicate that the cationic rhodium(I) complex indeed catalyzes the propargyl Claisen rearrangement. Furthermore, isolated allenic aldehyde 2a was indeed transformed to the corresponding dienal 3a at 80 °C (eq. 13). K. TANAKA et al.Scheme 3 A possible mechanism for the isomerization of allyl propargyl ether 1 to allenic aldehyde 2 and dienal 3.K. TANAKA et al.