TMSI-mediated Prins cyclization: diastereoselective synthesis of 4-iodo-2, 6-disubstituted tetrahydropyrans and synthesis of (±)-centrolobine

The reaction of aldehydes with homoallyl alcohols in the presence of TMSI generated in situ from TMSCl and NaI produced 4-iodo-tetrahydropyrans in good yields as a mixture of diastereo- isomers, which are separated and characterized. These iodo pyrans are reported for the first time. This methodology was extended to the synthesis of (±)-centrolobine