[89041-25-8] · C5H15CuSSn · Trimethylstannylcopper-Dimethyl Sulfide · (MW 289.53)
Physical Data: prepared in situ; its THF solution is deep red.
Solubility: sol THF.
Preparative Method: Me3SnCu.Me2S (2) is readily prepared1 by addition of solid CuBr.Me2S8 (see Copper(I) Bromide) to a solution of Trimethylstannyllithium (1)7b,9 in THF (eq 1). The actual structure of the stannylcopper(I) reagent is not known. Formula (2) is employed for convenience and on the basis of analogy with alkylcopper(I) reagents.
Handling, Storage, and Precautions: the reagent is sensitive to air and must be prepared in dry THF and used under an inert atmosphere. Since organotin compounds exhibit toxicity,7a reaction workup should be carried out only in a well-ventilated fume hood.
Reagent (2) is appreciably less reactive than the parent Me3SnLi (1). Although (1) efficiently effects conjugate addition of the Me3Sn function to a,b-unsaturated ketones and esters,1,9 (2) reacts with these substrates sluggishly or not at all.1 On the other hand, (2) is an excellent agent for the transformation of b-iodo a,b-unsaturated ketones10 into the corresponding b-trimethylstannyl enones (eq 2).1 The latter substances are potentially useful intermediates for organic synthesis.11
An important use of reagent (2) results in the regioselective cis addition of the elements of Me3Sn-H across the triple bond of a,b-alkynic esters2,5 and N,N-dimethylamides4 (eqs 3 and 4). Attempts to trap the intermediates derived from the ester substrates with electrophiles other than protons have not been successful.3 -5,12 On the other hand, the corresponding intermediates obtained from the amide substrates can be trapped with reactive alkylating agents (eq 4).4 The synthetic utility of alkyl (E)-3-trimethylstannyl-2-alkenoates (cf. 3) has been demonstrated in a variety of contexts.13
Interestingly, treatment of a,b-alkynic esters with reagent (2) under suitable conditions provides alkyl (E)-2,3-bis(trimethylstannyl)-2-alkenoates (eq 5).3 The latter compounds, which may also be prepared by Pd0-catalyzed addition of Hexamethyldistannane to a,b-alkynic esters,14a,c are useful substrates for the stereocontrolled preparation of tetrasubstituted alkenes.14b
Under appropriate conditions, Me3SnCu.Me2S (2) reacts with 1-alkynes to provide, regioselectively, 2-trimethylstannyl-1-alkenes6,15-22 (eq 6).15 This process can be carried out successfully in the presence of a variety of functional groups. Functionalized 2-trimethylstannyl-1-alkenes are useful intermediates for organic synthesis16-19,23 (see also 4-Chloro-2-trimethylstannyl-1-butene).
Edward Piers & Christine Rogers
University of British Columbia, Vancouver, BC, Canada