An Alkyne Hydrosilylation-Oxidation Strategy for the Selective Installation of Oxygen Functionality

Abstract

Alkynes bearing propargylic, homopropargylic, and bis-homopropargylic hydroxyl groups are shown to serve as precursors for ketone or α-hydroxy ketone functionality. The approach hinges on the intermediacy of vinylsilanes created through regioselective hydrosilylation catalyzed by the complex [Cp*Ru(MeCN) 3 ]PF 6 . Several oxidative pathways of linear and cyclic vinylsilanes are studied, and the possibility of diastereoselective epoxidation of cyclic vinylsilanes is demonstrated. The sequences constitute the equivalent of stereoselective aldol, homo-aldol, and bishomo-aldol type processes. The method is applied to a short synthesis of the piperidine alkaloid, spectaline.

Preparation of siloxacyclopentene containing 1,3-dienes and their Diels–Alder reactions

“…5 Other routes to siloxacycle containing species which have been used in cross coupling chemistry have also been reported previously. [6][7][8] In 2004, Clark and Woerpel reported the reaction of a "tBu 2 Si" source with a protected enynol to produce a siloxacyclopentene containing a silicon substituent at the 1 position of a 1,3 diene moiety. 9 This diene reacted with N-phenylmaleimide in a Diels-Alder reaction.…”

Application of the Aza-Achmatowicz Oxidative Rearrangement for the Stereoselective Synthesis of the Cassia and Prosopis Alkaloid Family

“…21 Finally, Trost and co-workers reported a route to (+)-spectaline (1) using a hydrosilylation-oxidation strategy. 22 Despite the availability of many synthetic methods for this class of compounds, there still exists a need to develop procedures more efficient than those currently in existence. In connection with our ongoing studies on natural product synthesis based on amidofuran chemistry, 23 we became interested in employing N-tosylaminofurans for the synthesis of various cis-2,3,6-trisubstituted piperidine alkaloids.…”

Asymmetric Total Synthesis of Soraphen A: A Flexible Alkyne Strategy

“…The use of aqueous H 2 O 2 , under conditions first reported by Hosomi and coworkers [22] that we have previously exploited for this transformation, [11] led to substantial amounts of protodesilylation. However, under anhydrous conditions developed in our laboratory, [11] using urea hydrogen peroxide complex (UHP) as oxidant, clean oxidation was observed in good yield with only small amounts of protodesilylation (ca 10-15%). The secondary TBS ether was not deprotected during the oxidation, and subsequent deprotection was achieved using HF·pyr to afford 17.…”

“…We have previously demonstrated the utility of epoxysilanes as masked α-hydroxyketones, wherein Tamao-Fleming oxidation of the epoxysilane conveniently unmasks this group. [11] Furthermore, these epoxysilanes are readily prepared from an alkyne functional group by hydrosilylation followed by epoxidation. Thus, an alkyne serves as a convenient synthon for an α-hydroxyketone facilitating C-C bond formation and minimizing the use of protecting groups.…”