Palladium‐Catalyzed Hydroalkynylation of Alkylidenecyclopropanes

Palladium-catalyzed hydroalkylation of methylenecyclopropanes with simple hydrazones

“…8 Consequently, reliable methods toward the facile generation of versatile terminal alkenes would be very desirable in organic synthesis. 9 Toward this target, some efforts have been focused on the hydrofunctionalizations of MCPs through selective C-C distal-bond cleavage, mostly developed by the groups of Yamamoto, 10 Shi 11 and Mascareñas, 12 with several types of pronucleophiles with relatively stronger nucleophilicity, such as nitrogen, oxygen and carbanion nucleophiles. As a result, a variety of functionalized terminal alkenes have been fabricated through these transformations.…”

Cobalt‐Catalyzed Hydroalkynylation of Vinylaziridines

“…Whereas a CF 3 group in para position of the phenylacetylene derivative did not allow the formation of hydroalkynylation products, enynes 3 al and 4 al, with a CF 3 in meta position were isolated, albeit in low yields, 13% and 10% respectively (entries 8 and 12). The cobalt-catalyzed hydroalkynylation was also found tolerant toward ester group in meta position (entry 13), 1-naphthylacetylene (entry 14), and alkynes containing a heterocycle such as 2-thienyl or 1-tosylindolyl (entries [15][16]. In all the above mentioned examples, no noticeable selectivity between linear and branched enynes was observed, and the E/Z selectivity in linear enynes 3 a was found moderate to good (4:1 to 10:1).…”

“…With benzylidenecyclopropane substrates and a palladium(0)/phosphite catalytic system, López and Mascareñas showed that the hydroalkynylation occured with a ring‐opening of the cyclopropane. The ratio of the resulting three isomers depended on the nature of the R 1 substituent (Scheme 1c) [15] . During the investigation of a platinum‐catalyzed [3+2] cycloaddition between alkylidenecyclopropanes and alkynes, [16] we observed, as a side reaction, an hydroalkynylation process leading to the distal bond cleavage of the alkylidene moiety.…”

Regiodivergent Synthesis of 1,3‐ and 1,4‐Enynes through Kinetically Favored Hydropalladation and Ligand‐Enforced Carbopalladation

“…Recently, Pd‐catalyzed oxidative cross‐coupling of N‐tosylhydrazones and diazoesters with alkynes and the Cu‐catalyzed tandem cross‐coupling of diazophosphonates, alkynes, and aldehydes for the synthesis of the same Z ‐stereoisomer were disclosed. Notably, the available synthetic routes to skipped 1,4‐enynes via a similar intermediate require an alkylidenecyclopropane, a 1,3‐diene,, and a hydroxyl or its derived leaving groups, for facile elimination in the reactions with alkynes (Scheme B). To develop more flexible synthetic routes, preparation of such enynes in an atom‐economical manner is highly desirable, whereby both of these can be accessed selectively by appropriate choice of a common structural motif.…”