Metathesis group-selective enyne

Group-selective enyne metathesis of dienyne 127f having a large substituent on the alkyne proceeds in the presence of aUcene 130 to give small ring compound 131... 

With this key union effected, only a few operations separated 48 from the substrate needed to test enyne metathesis (i.e. 12, Scheme 9). First, the controlled exposure of this compound (48) to 2 equivalents of TBAF in THF at 0°C effected the lysis of both the phenolic silyl ether and the TMS group append onto the terminal position of the alkyne, but, importantly, not the TIPS group on the other acetylene group. As such, in the next operation partial reduction with Lindlar s catalyst (Pd on BaS04 poisoned with quinoline) was accomplished selectively on only one alkyne to provide the needed terminal olefin. Finally, cleavage of the alky-nyl TIPS moiety under more forcing conditions (TBAF, THF, 25 °C), followed by silylation of both the allylic hydroxy and the phenolic groups (TBSCl, imid, DMF), then completed the assembly of enyne metathesis precursor 12 in 62% overall yield from 48. 

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