Stereoselective synthesis of 4-alkoxy-3-methylidenealkanols using reactions between 2-(1-alkoxyalkyl)propenylstannanes and aldehydes: X-ray crystal structure of (1R,4R)-3-methylidene-1-(4-nitrophenyl)pentane-1,4-diol

The 2-(1-hydroxy- and 1-alkoxy-alkyl)propenylstannanes 9 and 11-15, react with aldehydes to form 4-hydroxy- and 4-alkoxy-3-methylidenealkanols 23, 24 and 36-53, The stereoselectivity of these reactions has been investigated, If the reactions are carried out by transmetallation of the stannane using a tin(rv) halide before addition of the aldehyde, modest stereoselectivity in favour of the 1,4-anti-products 23, 36 and 37 is observed for the hydroxystannane 9, whereas the alkoxystannanes 11-15 give rise preferentially to the 1,4-syn-diastereoisomers 47-53, selectivity 75-85:25-15, It should be noted that these stereochemical assignments are the reverse of those reported in the preliminary communication on this work, The structure of the 1,4-anti-product 36 from the reaction between the hydroxystannane 9 and p-nitrobenzaldehyde was established by X-ray diffraction, The stereoselectivity of BINOL-titanium(Iv) catalysed reactions of the (R)-SEM-stannane (R)-12 with benzaldehyde is controlled by the configuration of the BINOL and can be used to synthesize either the 1,4-anti- or 1,4-syn-isomers 40 and 47.