[67132-62-1] · C3H9AlSe · Dimethylaluminum Methylselenolate · (MW 151.04)
(preparation of methyl selenoesters; aldol condensation of enones)
Solubility: reaction are typically run in toluene.
Preparative Methods: conveniently prepared by heating a toluene solution of Trimethylaluminum with powdered Selenium for 2 h at reflux.2 The yellow-colored supernatant was transferred to a septum-capped argon-filled Erlenmeyer flask.
Handling, Storage, and Precautions: the reagent was found to retain its activity for approximately one month at rt. Selenium reagents are toxic and should be handled with caution, in a fume hood.
Methyl and ethyl carboxylates and lactones are converted into methyl selenoesters in almost quantitative yields (eq 1).2,3 While d-valerolactone and trans-2-hydroxycyclohexane acetic acid g-lactone were converted cleanly to hydroxy selenoesters, g-butyrolactone was recovered unchanged. Acetals and isolated double bonds were not affected. Thionoesters are also converted to thionoselenoesters in similar yields.4,5
Methyl cis- and trans-cyclohexanedicarboxylates are converted to the corresponding selenoesters without enolization (eq 2).6 The conversion seems to be sensitive to steric factors, allowing selective transformation of one ester group in the presence of others (eqs 3 and 4).6 t-Butyl and trimethylsilyl esters are unreactive.
Selenoesters react with various nucleophiles to afford acids (water), esters (alcohols), and amides (amines).3 Ketones, including enones, were prepared in excellent yields from selenoesters and organocuprates.6,7 Selenoesters gave slightly higher yields compared to corresponding acid chlorides.7 While organomanganese and organoboronates were also effective, organocadmium and organomercury compounds were not effective.
Selenoesters afford 2-unsubstituted oxazoles upon reaction with various isocyanides in the presence of copper(I) salts and Triethylamine or 1,8-Diazabicyclo[5.4.0]undec-7-ene.3 They are also mild acyl electrophiles in Friedel-Crafts reactions with Copper(I) Trifluoromethanesulfonate as catalyst (eq 5).3 Benzene was not acylated and toluene was acylated in low yield.
This reagent adds methylselenol to enones in 1,4-fashion. The intermediate, an aluminum enolate, undergoes aldol condensation with aldehydes (see Diethylaluminum Thiophenoxide) (eq 6).8,9 This reagent also converts d-alkylidene-d-lactones to 1,3-cyclohexanediones, probably via an aluminum enolate.10
Beckmann rearrangements of cyclododecanone and acetophenone oxime mesylates have been accomplished to afford an imino selenoether with 2 equiv of the title reagent (eq 7).11
This reagent can also open up oxiranes in preference to selenoester formation.2,3
Korea Research Institute of Chemical Technology, Daejeon, Korea