Access to the Protoilludane Core by Gold-Catalyzed Allene-vinylcyclopropane Cycloisomerization

Abstract

Gold(I)-catalyzed allene-vinylcyclopropane cycloisomerization leads to the tricyclic framework of the protoilludanes in a single step by a reaction that involves a cyclopropane ring expansion and a Prins cyclization.

Total Synthesis of (−)‐Glaucocalyxin A

“…To overcome this issue, ketone 9 was selectively reduced to the corresponding alcohol, which was subsequently protected with Ac 2 O to provide the acetate 24 . Removal of the TBS group of 24 with TASF proceeded smoothly to produce the corresponding alcohol which was then oxidized by DMP to yield ketone 25 . Reduction of the ketone 25 with Li in liquid NH 3 gave the desired diol 26 in 73 % yield .…”

Gold-Catalyzed Enantioselective Ring-Expanding Cycloisomerization of Cyclopropylidene Bearing 1,5-Enynes

“… 17 Compound 6 is similar in structure and stereochemistry to the russujaponol D family of natural products. 7 This mechanism also suggests an explanation for the poor behavior of the unsubstituted enyne in entry 9 (Table 1 ), which would cyclogenerate a secondary cation in the initiating 6- endo-dig cyclization. These data point to the viability (and trapability) of allylic carbocation 7 as a reactive intermediate during the gold-catalyzed ring-expanding cycloisomerization of 1,5-enynes.…”

“…Its synthesis has therefore attracted much attention, 4 including two gold-catalyzed cycloisomerization approaches that generate a key cyclopropylmethyl carbocation intermediate: 5 one cyclogenerated from 1,6-enynes (Toste) 6 and a second from 1,7-allene-enes (Echevarren). 7 As part of a program aimed at utilizing strain relief in alkylidenecyclopropanes to drive the rearrangement of unsaturated hydrocarbons, 8 we hypothesized that easily synthesized 1,5-alkynylalkylidenecyclopropanes like 1 would efficiently yield the [4.2.0]-skeleton and further be amenable to asymmetric catalysis (Figure 2 C). We now report a gold-catalyzed enantioselective ring-expanding cycloisomerization of 1,5-enynes 1 to chiral bicyclo[4.2.0]octadiene 2 (Figure 2 C).…”

Density functional calculations for Rh(I)‐catalyzed C–C bond activation of siloxyvinylcyclopropanes and diazoesters

“…Similar transformations have been conducted catalyzed both intra‐ and intermolecularly using many transition metals (e.g. rhodium, ruthenium, iridium, iron, nickel, palladium, gold).…”