Allylsilyl Propargyl Ethers as Substrates for Intramolecular Pauson–Khand Reactions

Abstract

Silyl ethers that are synthesized by coupling a propargylic alcohol with an allylsilyl chloride are shown to undergo sulfide-promoted Pauson -Khand reactions, affording bicyclic enones.

Pauson–Khand reaction of fluorinated compounds

“…Martínez-Solorio and co-workers reported an intramolecular PKR of Si−O tethered 1,7-enynes 35, affording cyclopentaoxasilinones 36 with high diastereoselectivity [56]. In contrast to previous silicon-based tethers, which reacted in low yields and resulted in unexpected byproducts, this transformation could be performed on a multigram scale and showed a wide substrate scope and functional group compatibility, as well as high diastereoselectivity [57,58]. In this work, Si−O tethered 1,7-enynes underwent the PKR after treatment with 1.05 equiv of Co 2 (CO) 8 using 4-fluorobenzyl(methyl)sulfide (4-FBnSMe) as an additive, which is commercially available and can be easily recovered by flash chromatography.…”

Recent advances in the use of temporary silicon tethers in metal-mediated reactions

“…31 However, siloxane linkers have been employed by Pagenkopf et al in an unusual alkenyl Pauson-Khand variation, whereby cobaltmediated cyclisation of tethered vinyl silanes such as 75 resulted in unexpected reductive cleavage of both the silicon and propargylic alcohol moieties (76) in all but two cases (Scheme 15). 32 More recently, both Ishaq and Porter 33 and Dobbs et al 31 have reported the cyclisation of allyl propargyl silyl ethers (e.g. 77), using either n-butyl methyl sulfide or NMO as promoters.…”

Five‐Membered Carbocycles

“…Several authors have reported on the use of silicon tethers to promote the PKR. [48][49][50] However, the success of the PKR varies considerably with the substituent pattern on the silicon, the alkene and the alkyne. Dobbs has explored the use of silyl ether, silyl acetal, and silyl alkyl tethers in the PKR.…”

“…The vinylogous 48 ynone cyclised in 62% yield to provide the tricyclic product 49 as a 2.7:1 mixture of cis/trans isomers. An interesting intramolecular example was disclosed by de Meijere in which ketone 50 Thus, under the appropriate conditions, the alkyne partner does not appear to be severly limited by electronics or sterics. It is important that the regiochemstry of the alkyne substituents in the products can be predicted with some confidence.…”