Development of intermolecular additive free Pauson–Khand reactions for estrone E-ring extension using microwaves

A Decade of Advancements in Pauson–Khand‐Type Reactions

“…A Pauson–Khand method was used as a protocol for an estrone E‐ring extension synthesis (Scheme ) 116. A series of alkynes could be used under these reaction conditions.…”

Five‐Membered Carbocycles

“…59 Microwave irradiation (MWI) has been reported as an effective way to promote the PKR. [60][61][62][63] Helaja described the use of MWI to promote the PKR for the synthesis of estrone derivatives, 27a and 27b. 60 MWI was equally effective at promoting the PKR as was i-butylmethylsulfide, but that the regioselectivity was inverted.…”

“…[60][61][62][63] Helaja described the use of MWI to promote the PKR for the synthesis of estrone derivatives, 27a and 27b. 60 MWI was equally effective at promoting the PKR as was i-butylmethylsulfide, but that the regioselectivity was inverted. Reaction yields were improved when the target temperature was no greater than 100 °C and the alkyne was added in portions.…”

Microwave-Accelerated Ruthenium-Catalyzed [2π + 2π] Cycloadditions of Dimethylacetylene Dicarboxylate with Norbornenes

“…Ruthenium-catalyzed reactions of olefins in microwave conditions are reported for olefin metathesis, [2 þ 2 þ 2] cyclotrimerization, and 1,6-diene and 1,6-enyne cycloisomerizations. [10] On the other hand, just a few examples exist of transition metal-catalyzed addition of various reagents to norbornenes (chromium complexes in C-C bond-forming [2 þ 2 þ 1]=[2 þ 1] addition), [11] Pauson-Khand reaction (with cobalt reagents), [12] and ring-opening methathesis of norbornenes employing Grubb's Ru catalysts. [13] These literature examples indicate the stability and suitability of various ruthenium catalysts to be used in microwave conditions.…”

“…Furthermore, the influence of amount of catalyst on the reaction outcome is analyzed. It was found that reduction of catalyst to 5% diminishes the reaction yield to 46% (entry 12). Surprisingly, when the amount of catalyst was doubled to 20%, almost identical yield was obtained (41%, entry 13).…”