Tin hydride reagent

The limited kinetic data for reactions of tin hydride with nitrogen-centered radicals apparently demonstrates the combined effects of the enthalpies of the reactions and polarization in the transition states for H-atom transfer. The aminyl and iminyl radicals are electron-rich, and the N-H bonds formed are relatively weak these radicals react relatively slowly with tin hydride. On the other hand, the electrophilic amidyl and aminium cation radicals form strong N-H bonds and react rapidly with the tin hydride reagents. 

Halobutyl)cyclobutanones form cyclooctanones when they are reduced with tributyltin hydride in the presence of 2,2 -azobisisobutyronitrile.3,5 216, 217 Iodides usually give better yields than bromides. It is essential to add the tin hydride reagent slowly over a period of several hours, to keep its concentration low and thus avoid side reactions. Examples are the reactions to give l,s 2,3 and 3.217 A further example is found in ref 216. 

Hadida S, Super MS, Beckman EJ, Curran DP, Radical reactions with alkyl and fluoroalkyl (fluorous) tin hydride reagents in supercritical C02, J. Am. Chem. Soc., 119 7406-7407, 1997. 

Tin hydride reagents have been commonly used in radical-chain reductions in synthetic organic chemistry. It was reported by Vedejs and coworkers134 that the amino tin hydride reagent [o-(dimethylaminomethyl)phenyl]dimethyltin hydride (48) did not reduce esters,... 

Other means for generation and annulation of aryl radicals involve treatment of A -(t>-bromophenyl)propylamides with BusSnH/AIBN, which gives 3-alkylideneoxindoles <2(X)0J(P1)763>, or exposure of A -allyl(t>-iodoanilines) to fluorous tin hydride reagents, affording indolines <1999JA6607>. A set of indolines, for instance 239, have been obtained by radical cyclization of precursors such as 240, which were derived from A -allylanilines (Equation 76) <1999TL2533>. 

Curran [81-83] first demonstrated the value of this approach by the successful reduction of 1-bromoadamantane using the fluorous-soluble tin hydride reagent, tris(2-(perfluorohexyl)ethyl)tin hydride 34, (Fi3C6CH2CH2)3SnH. The fluorous tin hydride reagent was synthesised in three steps from 2-perfluorohexyl-1 -iodoethane in an overall yield of 65% (Scheme 6). In an attempt to mimic the... 

Fig. 7. Multiplex synthesis using a perfluoroalkyl-derivatised tin hydride reagent.

Another approach to enantioselective reductions involves reactions with chiral tin hydrides. The helical chirality of the binaphthyl group has been taken advantage of in the design of chiral tin reagents. An example of an enantioselective reduction using chiral tin hydride 88 is shown in Eq. (13.26) [38]. The reduced products are formed in low enantiomeric excesses (41 % ee) and low chemical yields (often under 50%). These factors and the difficulty in synthesizing the chiral tin hydride reagents serve to diminish the utility of these types of enantioselective reductions thus far. 

The reduction of alkyl halides is routinely carried out using tin hydride reagents. In practice, all supported tin hydrides have proved to be applicable to this well-known reaction, but vary in the amount of resulting tin contamination and how easily they can be recycled (Scheme 5.5.12). °... 

The Barton deoxygenation (or Barton-McCombie deoxygenation) is a two-step reaction sequence for the reduction of an alcohol to an alkane. The alcohol is first converted to a methyl xanthate or thioimidazoyl carbamate. Then, the xanthate or ihioimidazoyl carbamate is reduced with a tin hydride reagent under radical conditions to afford the alkane. Trialkylsilanes have also been used as the hydride source. Reviews (a) McCombie, S. W. In Comprehensive Organic Synthesis Trost, B. M. Fleming, I., Eds. Pergamon Press Oxford, U. K., 1991 Vol. 8, Chapter 4.2 Reduction of Saturated Alcohols and Amines to Alkanes, pp. 818-824. (b) Crich, D. Quintero, L. Chem. Rev. 1989, 89, 1413-1432. 

Scheme 3.14 Examples of radical reductions by the fluorous tin hydride reagent 33. The reagent can be removed from the reaction mixture by organic-fluorous liquid-liquid extraction [2a, 3],...

Tin hydride reagents are versatile tools for the functionalization of alkenes and alkynes. Based on this concept, Nicolaou and coworkers developed a polymer-bound tin hydride (118) that reacts via Pd-catalyzed hydrostannylation (or nucleophilic attack on the tin chloride with a vinyl lithium) with alkynes to give alkenylstannanes [116]. After further transformation to derivatives 119, the resin-bound substrates undergo proteolytic traceless cleavage to yield unsubstituted alkenes 120. Alternatively, the stannane can be employed for intramolecular Shlle coupling to produce macrolactones 121 in the cleavage step (Scheme 16.28). 

Directed reduction. Simultaneous complexation of GaCl, to a carbonyl group and a donor (such as triple bond) activated the former toward regioselective attack by a tin hydride reagent. 

Desulfonylation. The removal of the sulfonyl moiety fromp-keto sulfones with this couple in the presence of AIBN in refluxing r-butanol relies on a free-radical process, apparently involving a tin hydride reagent. 

Special care is required to handle trialkyltin hydrides and the waste they generate, and standard laboratory purification techniques often leave toxic levels of tin compounds in the product [88]. The industrial application of these methods has been hindered by the need to remove these tin-containing contaminants. Methods catalytic in tin have been developed [89-91], and tin hydride reagents modified to make their removal easier [92-98], but the need for alternatives to tin... 

The platinum-catalysed cycloisomerization of ene-yne 6.272 to give diene 6.273 was employed in a synthesis of streptorubin 6.277 (Scheme 6.110). After cyclization, the more electron poor of the two double bonds was reduced using a palladium-catalysed reduction with a tin hydride reagent. The ketone 6.274 was reduced and the resulting alcohol was excised by the Barton-McCombie method. The resulting... 

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