Titanium(IV)-promoted Mukaiyama aldol-Prins cyclizations.

[reaction: see text] A new version of the Mukaiyama aldol-Prins (MAP) cyclization has been developed. Unsaturated enol ethers such as 3 were found to couple with aldehydes in the presence of TiBr(4) to give 4-bromotetrahydropyran products. This cascade reaction sequence leads to the formation of two new carbon-carbon bonds, a ring, and three new stereogenic centers. We expect this reaction to be a powerful new tool in synthesis.