[2155-73-9] · C12H27Sb · Tri-n-butylstibine · (MW 293.14)
(agent for making carbon-carbon bonds between a-halogeno carboxylic derivatives2 (or a-halo ketones)3 and carbonyl compounds in neutral conditions; can promote the cyclopropanation reaction between electron-deficient alkenes with dibromomalonate and its analogs;4 formation of quaternary stibonium salt)
Physical Data: bp 131 °C/12 mmHg; d 1.197 g cm-3.
Solubility: insol H2O, ethanol; sol ether, petroleum ether, THF etc.
Preparative Method: prepared from Antimony(III) Chloride and 3 equiv of n-butylmagnesium bromide in absolute ether.5
Handling, Storage, and Precautions: pyrophoric; store and handle under nitrogen. Use in a fume hood.
Phenyl-substituted stibonium salts are difficult to form by reaction of triphenylstibine with halides. Ylides with strong a electron-withdrawing groups in the alkylidene moiety can be prepared by reaction with diazo compounds, but they are unreactive to carbonyl compounds.6 In contrast, trialkylstibines react readily with halides, especially with a-halo carboxylic derivatives, to form quaternary stibonium salts which react with carbonyl compounds to form alkenation products (eq 1).1
When R = H, R1 = alkyl, R2 = H, and E = CO2Et (or CONEt2, COMe), the products are highly stereoselective; when R = H, R1 = alkyl, R2 = H, and E = CN, the (E):(Z) ratio of products is ca. 3:2.2
b-Hydroxy ketones can be synthesized in excellent yield by the reaction of a-bromo ketones with various aldehydes mediated by Bu3Sb in the presence of a catalytic amount of Iodine (2-4%).7
The reaction of Diethyl Dibromomalonate and its analogs with electron-deficient alkenes mediated by Bu3Sb takes places easily under mild conditions and gives cyclopropane derivatives in high yields (eqs 2 and 3).4
A Barbier-type reaction by means of Bu3Sb has been reported (eq 4).8 The erythro/threo ratio is approximately 2:1 to 3:1.
Since Sb has a greater tendency to form pentaalkyl derivatives than do P and As, treatment of quaternary stibonium with a strong nucleophilic base R´M affords pentaorganyl stiboranes (l5-stibanes).9 These react with aldehydes to give secondary alcohols (eq 5).10 In the presence of Aluminum Chloride, pentaorganylstiboranes react with ketones to give tertiary alcohols.11
The reaction of Bu3Sb with propargyl bromide (see Propargyl Chloride), bromo-2-butyne, and trimethylsilylpropargyl bromide gave allenic and alkynic stibonium salts. The pentaorganylstiboranes formed by reaction with BuM react with aldehydes to give alkynic or allenic alcohols as major products (eqs 6-8).12
With less nucleophilic bases such as Lithium Diisopropylamide or Potassium t-Butoxide, the quaternary stibonium salts give stibonium ylides. These react with carbonyl compounds to give alkenes (eq 9).13
A novel alkenation of diazo compounds with carbonyl compounds mediated by Bu3Sb and a catalytic amount of copper(I) halide has been reported (eq 10).14 Stibonium ylides have been suggested as possible intermediates in these reactions.15
Yao-Zeng Huang, Li-Jun Zhang & Zhang-Lin Zhou
Shanghai Institute of Organic Chemistry, China