Regiodivergent Medium-Ring Oxasilacycle Synthesis from Diallylsilanes

Abstract

Medium-ring (7-9 membered) oxasilacycles were synthesized by sequential electrophile-promoted rearrangement of diallylsilanes, etherification with an alkene-containing alcohol, and ring-closing metathesis (RCM). Depending on the choice of catalyst for the RCM, different oxasilacycle products could be obtained. The Grubbs first-generation catalyst cleanly afforded allyl ether oxasilacycles whereas the second-generation Grubbs catalyst selected for the regioisomeric cyclic enol ether, resulting from RCM followed by isomerization.Isomerization during RCM was suppressed by substitution at the allyl ether position.The use of homoallyl ether-or non-ether substrates, and/or the addition of benzoquinone also prevented isomerization during RCM, suggestive of a ruthenium hydride-based double bond migration mechanism. Both product subclasses represent useful synthetic intermediates. As an initial demonstration, this sequence was used to prepare the side-chain of the natural product psymberin, as well as a ulosonic acid analogue.

Regioselective Fluorohydrin Synthesis from Allylsilanes and Evidence for a Silicon–Fluorine Gauche Effect

“…As part of an ongoing program investigating new reactions of allylsilanes, − we observed that epoxysilanes, prepared by epoxidation of the corresponding allylsilane, are cleanly converted to the corresponding fluorohydrin upon treatment with triethylamine trihydrofluoride (HF·Et 3 N; Table ). Other HF sources such as Olah’s reagent (HF·Py) resulted in significant decomposition.…”

Regioselective Fluorohydrin Synthesis from Allylsilanes

“…As part of an ongoing program investigating new reactions of allylsilanes, [11][12][13] we observed that epoxysilanes, prepared by epoxidation of the corresponding allylsilane, are cleanly converted to the corresponding fluorohydrin upon treatment with triethylamine trihydrofluoride (HF•Et3N; Table 1). Other HF sources such as Olah's reagent (HF•pyridine) resulted in significant decomposition.…”