Stereoselective synthesis of tetrahydropyran and oxepane systems by the endo-cyclization of hydroxy styrylepoxides

Epoxide‐Opening Cascades in the Synthesis of Polycyclic Polyether Natural Products

“…These directing groups either stabilize (relative to an H atom) the desired transition states, enabling regioselective nucleophilic attack, or make the undesired cyclization route less energetically favorable by changing the electronic properties of the epoxide. Currently available methods for endo-cyclization of epoxides rely on effects of alkenyl, [22][23][24][25][26] alkynyl, [27][28][29][30] alkyl, [31][32][33] and silyl [34][35][36] substituents that stabilize the partial positive charge within the desired, fused transition state in the Lewis or Brønsted acid-catalyzed reactions (Scheme 1). The directing groups that promote endo cyclization by destabilization of the undesired spiro transition state include sulfones [37][38][39] and methoxymethyl substituents in combination with a lanthanoid Lewis acid [40][41][42] (Scheme 2).…”

Biomimetic Synthesis of Polyether Natural Products via Polyepoxide Opening

“…These directing groups either stabilize (relative to an H atom) the desired transition states, enabling regioselective nucleophilic attack, or make the undesired cyclization route less energetically favorable by changing the electronic properties of the epoxide. Currently available methods for endo cyclization of epoxides rely on alkenyl [20,[23][24][25][26], alkynyl [27][28][29], alkyl [19,30,31], and silyl [18,32,33] substituents that stabilize partial positive charge within the desired, fused transition state in the Lewis or Brønsted acid-catalyzed reactions (Scheme 15.1a). The directing groups that promote endo cyclization via destabilization of the undesired spiro transition state include sulfones [21,34,35], as well as methoxymethyl substituents in combination with a lanthanide Lewis acid [22,[36][37][38] (Scheme 15.1b).…”

Vinylepoxides in Organic Synthesis

“…In order to improve the selectivities in these reactions, styrylepoxides 39 and 40 were prepared and subjected to acid-catalyzed cyclizations (Scheme 9.23) [113]. Both compounds, however, afforded almost identical mixtures of diastereomeric oxepanes 41 and 42 (83 %, dr 21:79 and 66 %, dr 20:80, respectively), while no tetrahydropyran 43 was formed.…”