Highly Efficient Bond-Forming Reactions utilizing Ynolates

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We have found that ynolates react with ketones to afford β-lactone enolates, which are ring-opened to form tetrasubstituted olefins. In this research project, we investigated the details of the olefinations via ynolates including scope and limitations.1)Olefination of aryl alkyl ketones, aryl aryl ketones, and alkyl alkyl ketones : the olefination of aryl alkyl ketones gave the products with E-selectivity. In the case of aryl aryl ketones, the electron-rich aryl groups preferred to be positioned to be trans to carboxyl groups. Pinacolon furnished the olefin with Z-selectivity.2)Olefination of acylsilanes : Perfect Z-selectivity was achieved. This olefination giving vinylsilanes is the first successful efficient olefination giving tetrasubstituted olefins with high generality. The products are easily converted into other tetrasubstituted olefins. For examples, Hiyama coupling of the vinylsilanes with aryl iodide successfully provided the coupling products without adding fluoride. Becaus … More e of formation of hypervalent silanes by coordination of carbonyl oxygen, the Si-C bond is activated. Taking advantage the activation, novel synthesis of silalactones via electrophilic cleavage of C-Si bonds was found.3)Olefination of esters : it has been difficult in olefination of ester carbonyls by conventional reagents like Wittig reagents, due to the poor electrophlicity of the carbonyls. Ynolates easily react with esters to give the olefinated products (enol ethers) in good yield with high E-selectivity.The E/Z selectivity is determined by torquoselectivity in ring-opening (electrocyclic reactions) of the β-lactone enolates. The torquoselectivity is governed by 2^<nd> orbital interactions in the transition states. Theoretical calculations disclosed several orbital interactions : π-Orbitals of aryl groups and σ-orbitals of C-H bonds stabilize the σ^* orbital of the disconnecting C-O orbital in the transition states to make them rotate outward, σ^* Orbitals of C-Si, C-O, and C-C bonds stabilize the σ orbital of the disconnecting C-O bond to make them rotate inward. Less