[62086-04-8] · C2F6O6S2Sn · Tin(II) Trifluoromethanesulfonate · (MW 416.87)
(mild Lewis acid used primarily for the generation of tin(II) enolates for stereoselective aldol and Michael reactions;1 [2,3]-Wittig and Ireland-Claisen rearrangements;2 addition of tin(II) acetylides to aldehydes;3 asymmetric allylation of aldehydes4)
Physical Data: mp >300 °C.
Form Supplied in: fine white powder.5
Purification: can be purified by washing with diethyl ether.6
Handling, Storage, and Precautions: moisture and air sensitive; all handling and storage should be done under nitrogen.
Mukaiyama has developed the use of tin(II) triflate in diastereoselective and enantioselective aldol-type reactions.1,7 Initially, the stereoselective aldol reactions were demonstrated using a stoichiometric amount of tin(II) triflate.8 The reaction between 3-acylthiazolidine-2-thione and 3-phenylpropionaldehyde is a representative example of a diastereoselective syn-aldol synthesis (eq 1).
Enantioselective aldol-type reactions have been achieved by addition of a chiral diamine to the reaction mixture.9 Specifically, addition of (S)-1-methyl-2-[(piperidin-1-ylmethyl]pyrrolidine to the reaction of 3-acetylthiazolidine-2-thione and 3-phenylpropionaldehyde provides the syn-aldol with greater than 90% ee (eq 2).
Reactions of ketene silyl acetals with various aldehydes in the presence of a stoichiometric amount of a tin(II) triflate-tin(IV) additive-chiral diamine complex have also been performed with excellent enantioselectivity (eq 3).10
Stereoselective aldol reactions using a catalytic amount of tin(II) triflate have been developed. The diastereoselective reaction between Methyl Vinyl Ketone and benzaldehyde first demonstrated the usefulness of tin(II) triflate as a catalyst (eq 4).1
The development of catalytic enantioselective reactions of silyl enol ethers with aliphatic, aromatic, alkynic, and a,b-unsaturated aldehydes has broadened the scope of this catalytic process (eqs 5-7).7a,b
In addition, Mukaiyama has shown that the stereochemistry of these reactions is controlled by the tin(II) triflate-tin(IV) additive-chiral diamine complex and is therefore independent of the chirality of the aldehyde (eqs 8 and 9).7b,11
The development of catalytic aldol-type reactions led to the discovery of a tin(II) triflate-catalyzed asymmetric Michael reaction.1 Specifically, tin(II) enolates, prepared in situ from silyl enethiolates with catalytic amounts of tin(II) triflate and a chiral diamine, react with various a,b-unsaturated ketones to give chiral Michael adducts with 40-70% ee (eq 10).12 Previously, asymmetric Michael reactions of tin(II) enolates with enones had been demonstrated in stoichiometric systems (eq 11).13
Tin(II) enolates, generated from allylic glycolate esters and tin(II) triflate in the presence of Diisopropylethylamine, undergo [2,3]-Wittig rearrangements upon warming to room temperature (eq 12).2a The corresponding boron enolates of the esters rearrange in a similar manner but with less stereoselectivity.
An isolated case of an a-alkoxy ester rearranging via a tin(II) enolate has been reported (eq 13).2b
In the presence of a stoichiometric amount of tin(II) triflate, 1-alkynes react with aldehydes and ketones to give alkynic alcohols in 57-91% yield (eq 14).3 The mechanism of this reaction is, at present, unclear. It has been proposed that the tin(II) triflate reacts with the alkyne to form a tin acetylide which adds to the aldehyde.
Mukaiyama has designed a
chiral allylating agent consisting of an allyldialkylaluminum and a chiral diamine chelated to tin(II) triflate. The reaction of this agent with various aldehydes gives corresponding homoallylic alcohols with good to excellent enantioselectivity (eq 15).4 Other tin(II) compounds (SnCl2, SnBr2, SnF2, Sn(OAc)2) react in this system to give the homoallylic alcohols in good yield but with virtually no enantioselectivity.
Eli Lilly and Company, Indianapolis, IN, USA