Conjugated Additions of Selenium Containing Enolates to Enones – Enantioselective Synthesis of δ‐Oxo‐α‐Seleno Esters and Their Facile Transformations

Abstract

Titanium enolates derived from methyl phenylselenoacetate and other acetates bearing a selenium containing chiral auxiliary have been employed to bring about 1,4-addition reactions to enones. These reactions generate δ-oxo-α-seleno esters in good yields and with excellent regio-and diastereoselectivities. The results obtained clearly indicate that the Lewis acids, employed to activate the starting enones towards addition, greatly influence reactivity as well as the stereochemical outcomes of these reactions. TiCl 4 complex-

Product Class 6: Oxonium Salts

“…This cation is used as an electrophile susceptible to intramolecular [115][116][117] and intermolecular attack, as exemplified by the synthesis of alcohols 14 from alkylselanylsubstituted esters 13 (Scheme 10). [117] The selenonium ion is also used as a selanylating reagent [118] and the known selenopyranium ion condenses with carbonyls.…”

“…This cation is used as an electrophile susceptible to intramolecular [115][116][117] and intermolecular attack, as exemplified by the synthesis of alcohols 14 from alkylselanylsubstituted esters 13 (Scheme 10). [117] The selenonium ion is also used as a selanylating reagent [118] and the known selenopyranium ion condenses with carbonyls. [119] Scheme 9 Preparation of an Epoxide [102] 65−75% 2-Hydroxy 5-Oxo Esters 14; General Procedure: [117] To a stirred mixture of the selenide 13 (0.2 mmol) and CH 2 Cl 2 (5 mL) at rt was added Me 3 OBF 4 (0.4 mmol) under N 2 .…”

“…[117] The selenonium ion is also used as a selanylating reagent [118] and the known selenopyranium ion condenses with carbonyls. [119] Scheme 9 Preparation of an Epoxide [102] 65−75% 2-Hydroxy 5-Oxo Esters 14; General Procedure: [117] To a stirred mixture of the selenide 13 (0.2 mmol) and CH 2 Cl 2 (5 mL) at rt was added Me 3 OBF 4 (0.4 mmol) under N 2 . After 2 h, the CH 2 Cl 2 was removed under reduced pressure.…”

Titanium Enolate Chemistry at the Beginning of the 21st Century

“…In contrast, very high diastereoselectivities were observed for addition of titanium(IV) enolates derived from methyl phenylselenoacetate 64 to enone 65 . The described procedure led to new δ‐oxo‐α‐seleno esters 66 in good yields (Scheme ) 101a. More recently, application of protected α‐hydroxy ketones led to the 2,4‐ anti ‐4,5‐ anti dicarbonyl adducts in good yields and with excellent diastereomeric ratios 101b…”

Enantioselective synthesis of heterocyclic compounds mediated by organoselenium reagents

“…In a recent work we have described the conjugate additions of selenium containing enolates to enones. 15 In this case we used the camphor diselenide 3. These reactions were highly diastereoselective and only the syn adducts 10 were obtained.…”