[4104-89-6] · C21H18Sn · 3-Triphenylstannyl-1-propyne · (MW 389.10)
(addition of a propargyl or an allenyl group to aldehydes; reacts with alkyl halides to give a terminal allenyl or propargyl group; preparation of allenyl iodides and allenyl(aryl)iodinanes; isomerizes to triphenylstannylpropadiene in the presence of Lewis acids or electron donor solvents)
Alternate Name: triphenyl-2-propynylstannane; triphenylpropargylstannane.
Physical Data: mp 81-84 °C.
Solubility: typical reaction solvents include benzene and dichloromethane.
Analysis of Reagent Purity: reagent purity may be analyzed by 1H NMR.1 The most common impurity is the isomeric allene which may be detected by IR and 1H NMR.
Handling, Storage, and Precautions: organostannane reagents are highly toxic and readily absorbed through the skin. Proper safety equipment (i.e. fume hood, gloves, protective eyewear) should be utilized at all times when handling the reagent.2 Irradiation of 3-triphenylstannyl-1-propyne in C6D6 for 19 h resulted in isomerization to the allene. No isomerization was observed after heating in the dark at 70 °C for 7 h.3 Deliberate isomerization to the allene has also been accomplished by heating the propargylstannane in electron donor solvents or in the presence of Lewis acids.6
The addition of 3-triphenylstannyl-1-propyne to aldehydes has been reported to give mixtures of allenyl and propargyl products.4 Exclusive formation of the homopropargyl alcohol (b-acetylenic alcohol) may be obtained in an enantioselective manner by using the chiral bromoborane prepared from 1,2-diphenyl-1,2-diaminoethane (stilbenediamine).5 Treatment of triphenylpropargylstannane with the chiral bromoborane gave the allenylborane, which reacted with a variety of aldehydes to form homopropargyl alcohols with excellent enantioselectivity (eq 1).
Exclusive formation of a-hydroxy allenes (a-allenic alcohols) was accomplished by using an allenylstannane, tributylstannylpropadiene, which was prepared by isomerization of the corresponding propargylstannane.5 Isomerization of 3-triphenylstannyl-1-propyne to its allenyl derivative, triphenylstannylpropadiene, is also readily accomplished in the presence of Lewis acids or electron donor solvents.6
See also 3-Iodo-1-trimethylsilylpropyne for the preparation of trimethylsilyl substituted a-allenic and b-acetylenic alcohols.
Baldwin et al. report the formation of terminal allenes from the reaction of 3-triphenylstannyl-1-propyne with alkyl bromides and iodides in the presence of Azobisisobutyronitrile in refluxing benzene (eq 2).7 In a related study, Hamon et al. report the formation of terminal alkynes with high diastereoselectivity from the reaction of the propargylstannane with the 8-phenylmethyl ester of N-Boc-2-bromoglycine (eq 3).8 Both reactions are believed to involve radical intermediates; however, nucleophilic addition of the propargylstannane to an intermediate iminium species has also been proposed for the latter reaction (eq 3).
Allenyl iodides have been prepared by Iodine treatment of 3-triphenylstannyl-1-propyne (eq 4).9 Other carbon-tin bond cleavage reactions using Thiocyanogen (SCN)2 and Sulfur Dioxide are also known, giving the allenyl sulfide and the sulfur dioxide insertion product, respectively.10,11
Hypervalent allenyl(aryl)iodinanes have been prepared by reaction of the propargylstannane with aryliodinanes (eq 5).12 The product then undergoes a reductive iodonio-Claisen rearrangement to yield o-propargyliodoarenes.
Carol K. Wada
Indiana University, Bloomington, IN, USA