Synthesis of six-membered cyclic siloxanes via enyne metathesis with a ruthenium catalyst generated in situ

Abstract

The catalytic system in situ generated by combination of [RuCl 2( p-cymene)] 2 as a ruthenium source, 1,3-bis(mesityl)imidazolinium chloride (MesH 2ImCl) as a bulky electron-releasing carbene precursor and cesium carbonate as a base, is shown to be an efficient catalyst for the metathesis reaction of propargylic allylsilyl ethers R 1CCCR 2OSiMe 2CH 2CHCH 2. The metathesis products, the cyclic siloxanes, were obtained after complete conversion of the enynes in 67–87% isolated yields. These six-membered ring compounds contain the 1,3-diene unit that is used in Diels–Alder reaction and give access to heterobicyclic derivatives. The resulting cyclic siloxanes are selectively opened under oxidative conditions with H 2O 2 to afford allylic diols, with fluoride to form conjugated triene and under hydrogenation conditions with Pd/C catalyst to give a tetrasubstituted alkene.