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The Wittig reaction between (1-adamantylmethylidene)triphenylphosphorane and benzaldehyde leads to oxaphosphetanes with a cis/trans ratio of 74:26. The equally formed cis and trans oxaphosphetane intermediates decompose differentially. The cis form decomposes 7-12 times faster than the trans form. The reactions of the nonstabilized ylides involve an electron-transfer pathway. For sterically demanding ylides and substrates, the radical combination is the rate-determining step.

The Wittig reaction of benzaldehydes with benzylidenetriphenylphosphoranes passes through a highly nucleophilic polar cycloaddition state. The reactions register positive kinetic isotope effects and Hammet rho values, with and without lithium ions. The stereochemistry of the products is largely unaffected by reactant concentration, the ylide/aldehyde ratio nor by the mode of addition. Lower temperature, on the other hand, favors the formation of cis-products while ortho-position substituents affect the cis/trans ratio. The latter effect is probably due to chelation between the substituent and the ylide phosphorus.