Epoxy enynes

Liu has reported recently a new Co2(CO)8-mediated tandem [5+ 1]/ [2 + 2+ 1]-cycloaddition reaction that gives tricyclic 5-lactones from cis-epoxy enynes 186. This process possibly involves an initial opening of the epoxide in the cobalt hexacarbonyl complex 187 to from the complexed al-lene 189 via 188. Further coordination of the tethered olefin leads to 190 and further oxidative cyclization gives cobaltacycle 191 which inserts CO leading to the final compound 192. When performing the reaction under N2,191 suffers a reductive elimination to give cyclobutane 193 (Scheme 55) [172],... 

Cyclocarbonylation. An intriguing transformation of certain epoxy enynes entails double carbonylation and cycUzation. ... 

Epoxy enynes. The coupling of enol triflates with epoxyalkynes is catalyzed by Agl-PdCPPhj) (5 examples, 52-90%). 

Some of the most exciting investigations reported in recent months have been directed toward the direct diastereo- and enantioselective preparation of polycarbocychc products. Rai-Shung Liu of National Tsing-Hna University has extended (J. Org. Chem. 2007, 72, 567) the intramolecular Pauson-Khand tyclization to the epoxy enyne 16, leading to the 5-5 product 17. Michel R. Gagne ofthe University ofNorth Carolina has devised (J. Am. Chem. Soc. 2007,129, 11880) a Pt catalyst that smoothly cychzed the polyene 18 to the 6-6 product 19. Yoshihiro Sato of Hokkaido University and Miwako Moii of the Health Science University of Hokkaido have described (J. Am. Chem. Soc. 2007, 129, 7730) a Ru catalyst for the cycUzation of 20 to the 5-6-5 product 21. Each of these processes proceeded with high diastereocontrol. 

During modei studies for the synthesis of botrydiane sesquiterpene antibiotics, B.M. Trost and co-workers prepared a compiex 1,6-enyne precursor for transition metal catalyzed enyne metathesis reactions. The 1,6-enyne was prepared from a heavily substituted alkynal, which was synthesized via the Eschenmoser-Tanabe fragmentation of an epoxy ketone. The resulting alkynal was unstable, so it was immediately subjected to a Wittig oiefination to afford the desired 1,6-enyne. 

A novel route to biaryls has been reported starting from 1,4-epoxy-1,4-dihydroarenes. These substrates participate in a symmetrical coupling reaction in the presence of Pd(dba)2, Zn, and HSiCls (eq 28). Finally, a heterogeneous catalyst prepared from Pd(dba)2 and a phosphine-containing polymer resin has been found to facilitate the cycloisomerization of enynes in water. ... 

Epoxy-cyclo-octa-l,3,5-triene reacts with ethynylmagnesium bromides to give ethynylcycloheptatrienyl carbinols (239) which were converted by thionyl chloride into enynes (240). ... 

The scope of regio- and stereo-selective synthesis of vinylallenes by 1,5-(>S )-substitution of enyne acetates and oxiranes with organocuprates has been explored the products are usually obtained as mixtures of E- and Z-isomers (Scheme 12), ° Optimum conditions for stereoselective alkynylation of trans-2,3-epoxy sulfides at C(2), with double inversion of configuration, on reaction with alkynylaluminiums (Scheme 13) have been sought. 

---