Desymmetrization of 1,4-Dien-3-ols and Related Compounds via Ueno−Stork Radical Cyclizations

Abstract

[formula: see text] Desymmetrization of 1,4-dien-3-ols and related compounds via Ueno-Stork radical cyclizations is reported. The stereochemistry of the cyclization is controlled by the acetal center. Excellent stereocontrol at C(4) and C(5) of the newly formed tetrahydrofuran rings is observed. Use of a chiral auxiliary allows the preparation of enantiomerically pure material. The utility of this method has been demonstrated by achieving a short synthesis of (+)-eldanolide, the pheromone of the male African sugarcane stem borer Eldana saccharina.

An Entry to Curcuphenol/Elvirol Core Structures via a retro‐Aldol Reaction

“…Thus, submission of 5a , 5b , 5d , and 5g to an excess of the Wittig reagent (aldehyde : ylide (1 : 2)) at −78°, then r.t., for 30 min., provided 6a , 6b , 6d and 6g in good yields [22]. Under these reaction conditions and based on pKa value, phenols 5 can be deprotonated by the ylide, at least in part.…”

Diastereoselective Radical‐Mediated Hydrogen‐Atom Abstraction

“…For instance, by using acetals of type 1 and 3, it is possible to activate alcohols at the b position. The chromatographic resolution of the starting acetals and the use of a chiral auxiliary to control the absolute stereochemistry at the acetal chiral center [11,13,[21][22][23] should facilitate access to optically pure polysubstituted tetrahydrofurans and g-lactones. Further work toward this goal is currently underway.…”

“…[10] The stereochemical outcome of these reactions will be then compared with that of the selective cyclization of the related systems D to E, which has been thoroughly investigated by us (Scheme 1 b). [11][12][13] The radical precursors were readily prepared from the corresponding alcohols, 1-methoxyallene, and N-bromo-or N-iodosuccinimide, according to Equation (1). [14] The reaction conditions for the hydrogen abstraction were optimized with substrate 1 a [Eq.…”

Diastereoselective Radical‐Mediated Hydrogen‐Atom Abstraction

“…The two hydrogen atoms H a and H b are diastereotopic, and hydrogen‐atom abstraction can produce two diastereomeric radicals B and B′ that cyclize to produce the tetrahydrofurans ( r ‐2, c ‐5)‐ C and ( r ‐2, t ‐5)‐ C , respectively 10. The stereochemical outcome of these reactions will be then compared with that of the selective cyclization of the related systems D to E , which has been thoroughly investigated by us (Scheme ) 11–13. The radical precursors were readily prepared from the corresponding alcohols, 1‐methoxyallene, and N ‐bromo‐ or N ‐iodosuccinimide, according to Equation (1) 14…”