Dehalogenation tributyltin hydride

In the presence of AIBN, tributyltin hydride is an excellent dehalogenating reagent for generating radicals. The bromoalkylcyclobutanone 206 undergoes reductive ring expansion to give, via the annealed alkoxy radical, the cis-fiised bicycle 207 stereospecifically as the major product [113], (Scheme 81)... 

Mechanism of the radical chain dehalogenation of alkyl halides by tributyltin hydride. The various termination steps are not shown. 

Radical Dehalogenation of an Alkyl Halide with Tributyltin Hydride Section 21.7 Figure 21.3... 

Reductive dehalogenation with tin hydrides can be carried out without interference of a number of functional groups. However, a C-C double bond in a 1,5 relationship to the intermediate cyelopropyl radical can function as a trap and result in formation of bicyclo[3.1.0]hexane derivatives. Thus, treatment of l,l-dibromo-2-(but-3-enyl)cyclopropane with tributyltin hydride afforded a 15 85 mixture of l-bromo-2-(but-3-enyl)cyclopropane (13) and 1-bromo-2-methyl-bicyclo[3.1.0]hexane (12). Under similar conditions l-bromo-2,8,8-trimethyltricyclo-[3.2.1.0 ]octan-3-one (15) was obtained in 6% yield from an isomeric mixture of 7,7-dibromo-4-isopropenyl-l-methylbicyclo[4.1.0]hept-2-one the main product, isolated in 86% yield, was an isomerie mixture of 7-bromo-4-isopropenyl-l-methylbicyclo[4.1.0]hept-2-one (14). ... 

The halogen atom of an alkyl halide can be replaced by the hydrogen atom bonded to tin in tributyltin hydride (BUsSnH). The process, called dehalogenation, is a radical reaction, and it can be initiated by AIBN (2,2 -azobisisobutyronitrile). AIBN decomposes to form nitrogen gas and two isobutyronitrile radicals, which initiate the reaction. Write a mechanism for the reaction. 

Room temperature imidazolium ionic liquids have been shown to be useful solvents for the Michaelis-Arbuzov rearrangement, sometimes allowing the reaction to be performed at room temperature in a short period of tirne. Halolactones, which are the products of halolactonisation of y,5-unsaturated acids, have been shown to be dehalogenated by trialkyphosphites in the presence of water. This makes a useful alternative to the commonly used reduction by tributyltin hydride. The reactions of dibromoethane and dibromopropane with silyl phosphites have been studied. Mono and diphosphonoalkanes (37) and (38) were prepared and their chemical properties were studied. In the reaction of trifluoromethylated P-alkoxyketones with tris(trimethylsilyl)phosphite, a mixture of the 1,2- and 1,4-adducts (39) and (40) is produced. 

Carretero s chiral 2,6-a5-disubstituted piperidin-4-one intermediate (+)-1423," "" used in the previously described synthesis of (+)-lasubine II (e i-1342) (cf Scheme 180), also made an appearance in a synthesis of (+)-lasubine I (e i-1341) (Scheme 187). In this variant, detosylation of 1423 to (—)-1466 was followed by N-alkylation with l-chloro-4-iodobu-tane and halogen exchange of the alkylated product with sodium iodide under Finkelstein conditions to give the iodo product (—)-1467. The free-radical species generated by treating 1467 with tributyltin hydride in the presence of AIBN underwent fairly efficient (69%) diastereoselective cychzation to the ketone (+)-e i-1377, but also produced a small quantity (16%) of the dehalogenated product (—)-1468. The ketone was reduced in... 

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