Dedicated to Prof. Dieter Enders on the occasion of his 70th birthday
Abstract
The Prins reaction is an efficient method for the direct generation of 1,3-dioxanes
from alkenes and aldehydes. As first published in 2008, this process can be effected
by stoichiometric amounts of molecular iodine. We herein report a catalytic protocol allowing the use of iodine at low loading (0.5–5 mol%), smoothly effecting
the condensation of styrenes with aliphatic aldehydes to rac-1,3-dioxanes. Moreover, this mild catalytic system effects the isomerization of the
1,3-dioxane products to the thermodynamically favored one. As a result, substituted
rac-1,3-dioxanes were prepared in high yields (up to 92%), and with high diastereoselectivities
(d.r. up to 82:18). For the application of iodine in catalytic amounts, the addition
of pyridinium bis(trifluoromethanesulfonyl)imide (TFSI) salts in a 1:1 ratio to iodine
is the key to success.
Key words
Prins reaction - catalysis - 1,3-dioxanes - molecular iodine - bis(trifluoromethanesulfonyl)imide
salts