Functional group transformations peroxides

Chapter 11 focuses on aromatic substitution, including electrophilic aromatic substitution, reactions of diazonium ions, and palladium-catalyzed nucleophilic aromatic substitution. Chapter 12 discusses oxidation reactions and is organized on the basis of functional group transformations. Oxidants are subdivided as transition metals, oxygen and peroxides, and other oxidants. 

Condensation of 911 with ketophosphonate 913, prepared in 92% yield from 912, provides enone 914 in 88% yield. Subsequent functional group transformation converts 914 to the labile bis-cyclic carbonate 915. Treatment of 915 with a large excess of dimethyl sulfide in the presence of benzoyl peroxide followed by basic hydrolysis provides the tetraol 916. When 916 is treated with trimethylorthoacetate in the presence of catalytic PPTS followed by tri-methylsilyl chloride in a triethylamine buffer, the exclusive product is the diacetoxy dichloride 917. Base-mediated saponification of cmde 917 results in spontaneous cyclization to the bis-trans-QpoxidQ, which after treatment with a large excess of mercury(II) chloride affords (— )-depudicin (918) in 52% yield. The total synthesis involves 22 steps, and provides 918 in 1.4% overall yield [255] (Scheme 198). 

Functional group transformations are required because no additional carbon-carbon bonds must be formed. Bromides and alkyl halides in general can be formed from alkenes by reaction with HX (HBr in this case). If 52 reacts with HBr, however, the product is 2-bromo-2-methylpropane rather than 54 (Chapter 10, Section 10.2). It is possible to react HBr with an alkene in the presence of a peroxide (Chapter 10, Section 10.8.2) to give a primary bromide. However, if it is recognized that a bromide is prepared from an alcohol, then 54 may be prepared from 55, which is directly available from 52 by hydroboration (Chapter 10, Section 10.4.3). 

Another transformation hinging on the use of stoichiometric amounts of peroxide is an exchange reaction that replaces the xanthate group with a bromide. This synthetically valuable functional group exchange is illus-... 

Oxidation of bicyclic borane (2) with hydrogen peroxide in the presence of base leads to 1,5,9-nonanetriol (15) (Scheme 3) . It should be stressed that the combination of the three consequent reactions (hydroboration-pyrolysis-deboration) results in a unique approach for the transformation of monoalkenes to organic compounds containing three functional groups. Thus, a mixture of nonenes can be converted to 1,5,9-nonanetriol (15). 

The products of hydroboration—organoboranes—can be elaborated to a variety of organic functional groups, making hydroboration one of the most powerful synthetic reactions. The strategy in all such transformations involves adding a nucleophile to the Lewis-acidic boron, which makes it into an anionic center. In hydroboration-oxidation, the nucleophile is typically alkaline hydrogen peroxide ... 

Organoboranes are formed from the reaction of alkenes and BHg or, in some cases, with other organoboranes. Are organoboranes useful in other reactions The experimental example in Section 10.4.3 reports that monoalkylboranes 56 and 57 are converted to alcohols 52 and 53 by treatment with hydrogen peroxide and sodium hydroxide. This transformation is a formal oxidation (see Chapter 17). Several other reactions can transform an alkylborane into different functional groups, but this chapter will focus only on oxidation to an alcohol. 

---