Ozonolysis vinyl silane

Initially we chose to test elements of this approach to artemisinin in an abbreviated version of 4 that lacked the 2P-(3-oxobutyl) and 3a-methyl groups. Hence, on low-temperature ozonolysis of the vinyl silane 5 in methanol, transient and stereoexclusive formation of dioxetane 6 was observed upon immediate analysis by NMR (Eq. 3). On standing, the dioxetane 6 underwent rearrangement and cyclization to furnish hydroperoxy-lactone 7 in 54% isolated yield on a scale sufficient for X-ray structural study.44... 

As shown in Scheme 17,180 was available from the common, totally synthetic, intermediate 17. Using reported methodology for the introduction of vinylsilanes,57 17 was reacted smoothly with (methoxy dimethylsilyl) trimethylsilyl methyl-lithium in pentane to afford (EIZ) vinyl silane 220 in 54% yield. The main by-product in this reaction was ketone 17, which could be recycled thus, based on recovered 17, the yield of 220 was 93%. Hydrolysis of ketal 220 occurred without protodesilylation upon exposure to aqueous oxalic acid absorbed onto silica gel to give ketone 221 in 80% yield. Upon low-temperature ozonolysis of 221 in methanol, a remarkably stable dioxetane 223 was produced, as evidenced in the H NMR... 

The vinyl group has been used to protect the nitrogen of benzimidazole during meta-lation with lithium diisopropylamide. It is introduced with vinyl acetate [Hg(OAc)2, H2SO4, reflux, 24 h] or dibromoethane (TEA, reflux 10% aq. NaOH reflux) and cleaved by ozonolysis (MeOH, —78°C) or KMn04 (acetone, reflux, 99% yield). Both vinyl silanes and vinyl borates can be used to introduce the vinyl group on to heterocyclic amines. ... 

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