Abstract
Iodine-catalyzed Prins cyclization of homoallylic alcohols and ketones was investigated. Anhydrous conditions and inert atmosphere are not required in this metal-free protocol. The reaction of 2-(3,4-dihydronaphthalen-1-yl)propan-1-ol with six aliphatic symmetric ketones gave the desired products in 67-77% yield. Cyclization was performed with four aliphatic unsymmetric ketones, leading to corresponding pyrans in 66-76% yield. Prins cyclization was also accomplished with four aromatic ketones in 37-66% yield. Finally, Prins cyclization of the monoterpene isopulegol and acetone was successfully achieved.
Highlights
Prins cyclization constitutes a powerful tool to obtain tetrahydropyrans (Scheme 1),[1,2,3] including the key step in several total syntheses.[4,5,6,7,8,9,10,11,12,13,14] Typically, Prins cyclization is performed mixing a homoallylic alcohol and an aldehyde in the presence of excess of an acid under anhydrous conditions
The desired Prins cyclization product 3a was obtained in 76% yield using 5 mol% of iodine (Table 1, entry 1)
The step was the study of unsymmetrical ketones (Table 2)
Summary
Prins cyclization constitutes a powerful tool to obtain tetrahydropyrans (Scheme 1),[1,2,3] including the key step in several total syntheses.[4,5,6,7,8,9,10,11,12,13,14] Typically, Prins cyclization is performed mixing a homoallylic alcohol and an aldehyde in the presence of excess of an acid under anhydrous conditions.
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