[112621-93-9] · C8H12CuLi2NSSn · Dilithium (Trimethylstannyl)(2-thienyl)cyanocuprate · (MW 350.37)
Solubility: sol THF.
Preparative Method: the higher-order cuprate (Me3Sn)(2-Th)Cu(CN)Li2 (1) (Th = thienyl) can be prepared by the treatment of a solution of Hexamethyldistannane and thiophene in dry THF with Methyllithium, followed by addition of solid Copper(I) Cyanide (eq 1).1 Although the actual structure of the reagent is not known, formula (1) is used for convenience and to show stoichiometry. Analogous formulations have been employed for higher-order alkylcuprates.4 A solution of the reagent in THF is bright yellow in color.
Handling, Storage, and Precautions: the reagent should be prepared using dry THF under an inert atmosphere. Since organotin3 and cyanide compounds are toxic, work-up of reactions employing the reagent should be carried out in a fume hood.
Reagent (1) effects efficient conjugate addition of the Me3Sn function to a,b-unsaturated ketones, aldehydes, and esters (eqs 2 and 3).1 In this type of reaction, (1) appears to be less reactive than Me3SnLi5,6 but more reactive than the lower-order cuprate Me3SnCu(SPh)Li (6) (see Lithium Phenylthio(trimethylstannyl)cuprate). Thus Me3SnLi converts (4) into (5) under conditions5 much milder than those indicated in eq 3, while reagent (6) fails to react with (4).6
Reagent (1) is useful for the stereoselective conversion of a,b-alkynic esters into alkyl (Z)-3-trimethylstannyl-2-alkenoates.1 Although the lower-order cuprate (6) also effects this type of transformation,7 reactions of (6) with substrates containing an ether function on the g-carbon produce mainly the products of PhS transfer.7 This difficulty is avoided by utilization of reagent (1) (eq 4).1,8 Interestingly, the intermediate derived from the reaction of (7) with (1) can be trapped with reactive alkylating agents (eq 5).1 An intramolecular version of this process has also been achieved (eq 6).1
A number of higher-order mixed (trialkylstannyl)cyanocuprates related in structure to (1) have been reported. These reagents, which include the (trimethylstannyl)cuprates (Me3Sn)(R)Cu(CN)Li2 (8) (R = Me)9 and (9) (R = Bu)9,10 and the (tributylstannyl)cuprates (Bu3Sn)(R)Cu(CN)Li2 (10) (R = 2-Th),2,11 (11) (R = Me),12,13 and (12) (R = Bu),14-16 have been prepared via a variety of interesting methods9-14 and have been shown to be excellent sources of the Me3Sn and Bu3Sn moieties in reactions with an impressive array of electrophilic substrates. Representative examples are given in eqs 7-11.9,10,13,14,16
Edward Piers & Christine Rogers
University of British Columbia, Vancouver, BC, Canada