Dehydrative Re₂O₇-Catalyzed Approach to Dihydropyran Synthesis

Abstract

Monoallylic 1,3-and 1,5-diols undergo Re 2 O 7mediated ionization to form allylic cations that engage in cyclization reactions to form dihydropyran products. The reactions give the 2,6-trans-stereoisomer as the major products as a result of minimizing steric interactions in a boat-like transition state. The results of these studies are consistent with cationic intermediates, with an intriguing observation of stereochemical retention in one example.

Rhenium-catalysed reactions in chemical synthesis: selected case studies

“…More recently, the same group reported a germane dehydrative [Re 2 O 7 ]-catalysed approach for the synthesis of dihydropyrans from monoallylic 1,3-or 1,5-diols. 130…”

Perrhenate Esters as Intermediates in Molecular Complexity-Increasing Reactions

“…Jean-Marc Lawrence accepted the challenge of reducing this idea to practice, and a subset of his efforts is shown in Scheme 12. 40 A nuance of these studies is that the thermodynamic requirement to form a (Z)-alkene in the products mandates the allylic cation intermediate to exist in a cisoid conformation. This leads to the need for hexafluoroisopropyl alcohol (HFIP) to be used as part of a solvent mixture to prevent pre-cyclization cation decomposition and causes the reaction to proceed through a boat-like transition state.…”

Stereoselective syntheses of 2-methyl-1,3-diol acetalsviaRe-catalyzed [1,3]-allylic alcohol transposition

“…, 4 , 5 ). Taking the inspiration from prior studies, 8,9 we report herein Re-catalyzed highly stereoselective allylic transposition of alcohols 1–3 (Scheme 1). With 1 mol% Re 2 O 7 as the catalyst, the operationally simple protocol permits stereoselective syntheses of 2-methyl-1,3- syn -diol acetals 4 ( anti , anti ) and 5 ( syn , syn ) in high yields from alcohols 1–3 .…”

“… 8 High regio-control can also be accomplished through capturing the alcohol group with a trapping agent, thereby shifting the equilibrium toward the desired direction. 9 …”