We are investigating asymmetric Horner-Wittig (HW) reactions, involving asymmetric beta substituted phosphine oxides and aldehydes, as a means of straight forward construction of three contiguous sp3-sp2-sp3 carbon stereocentres.     Contiguous array of stereogenic centers synthesises by a Horner wittig reactionHere we report the role of the configuration of asymmetric carbon atoms on the position beta to a phosphine oxide or the position alpha to an aldehyde on the cis/trans selectivity in the alkene formation.We have prepared a series of beta substituted phosphine oxides with varying steric bulkiness and have investigated the outcome of their reactions with a variety of aldehydes. Using a combination of X-ray crystallography and NMR we investigated the relative configuration of the products. Our results demonstrate that the steric bulkiness of the beta substituent can influence the stereochemical outcome of the HW reactions. Furthermore, the presence of aromatic rings in the aldehyde can bias the reaction through a potential pi-stacking of aromatic rings in the transition state.To showcase its utility, we used this methodology towards the synthesis of the lateral side chain of phytosterols, a group of naturally occurring molecules with an emerging significance in cancer treatment. ?       Synthetic application : Phytosterols

Application of the Horner-Wittig reaction to the construction of contiguous stereocenters

247th National Meeting (2014)

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