[64331-89-1] · C19H17LiSn · (Triphenylstannylmethyl)lithium · (MW 371.01)
(methylenation reagent for several carbonyl compounds1)
Solubility: sol several kinds of ethers; protonated in protic solvents.
Preparative Methods: iodine-lithium exchange of triphenylstannylmethyl iodide in dry ether with n-Butyllithium (98%).1 Triphenylstannylmethyl iodide can be obtained by the reaction of Chlorotriphenylstannane with Simmons-Smith reagent (Iodomethylzinc Iodide) in 66% yield.2
Purification: recrystallization of the precursor triphenylstannylmethyl iodide from hexane (white crystalline plates, mp 86-87 °C)
Handling, Storage, and Precautions: the precursor can be stored in a desiccator. Since organotin compounds are toxic, the experiment should be performed in a good fume hood and with gloves.
Like (Trimethylstannylmethyl)lithium, this reagent (1) is an effective methylenation reagent. The reagent reacts with ketones or aldehydes (2) to afford b-stannyl alcohols (3), which undergo Peterson-type elimination under acidic conditions (HClO4/MeOH, 20 °C or SiO2/THF, 20 °C, 56-68%, based on 3)3 or heating (110-175 °C) to produce methylene compounds (4). Overall yields are improved if the alcohols (3) are not isolated (eq 1 and Table 1).4
The analogous (tributylstannylmethyl)lithium can be generated by the same procedure (98-100%), and this reagent also methylenates esters.5 Note that the preparation of (triphenylstannylmethyl)lithium (1) by iodine-lithium exchange should be performed in ether. In THF, the yield of the desired lithium reagent is decreased, producing iodomethyllithium as byproduct (eq 2).6
Although the reagent (1) does not react with Allyl Bromide, a copper derivative (5) obtained from (1) and Copper(I) Chloride couples with allyl bromide to afford homoallylstannane (6) in 57% yield.6 This reaction is thought to proceed through the tandem oxidative addition-reductive elimination mechanism (eq 3).
However, an unsuccessful coupling reaction of the cyanocuprate reagent (8), prepared from (tributylstannylmethyl)lithium and Copper(I) Cyanide, with alkenyloxirane (7) has been reported, although the ordinary alkylcuprates react with (7) smoothly. The major reaction of (8) is the oxidative coupling of the cuprate to afford 1,2-bis(tributylstannyl)ethane (9) (eq 4).7
Triphenylgermylmethyllithium8 and triphenylplumbylmethyllithium3 have also been prepared. See also Trimethylsilylmethyllithium and (Diisopropoxymethylsilyl)methylmagnesium Chloride.
Tadashi Sato & Jun Fujiwara
Waseda University, Tokyo, Japan