Carbomercuration stereoselectivity

In another example, Hg(OTf)2 has been used for the stereoselective ring expansion of 116 to 117 with excellent stereospecificity for the (Z)-isomer (Equation (43)).156 Carbomercuration reactions have also been observed for derivatives such as 118, which possesses both an allylic silane as well as an alkynyl functionality. For 118, the reaction affords the 5-m -ring compound 119 as the (Z)-isomer. Formation of the (/. )-isomcr is disfavored because the bulk of the TMS group precludes an anti-attack (Equation (44)).157... 

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