Miscellaneous Cleavage Reactions

Sodium naphthalide induced fragmentation and ring opening in oxatricyclic substrate 149, Eq. 101. The allylic sulfate formed underwent elimination to produce an oxabicyclo [6.2.1 ] system containing a trans olefin. Simple reduction and elimination of sulfate led to the minor product [149]. 

Cleavage of Carbon-Oxygen Bonds in the Oxabicydic Framework 

The cleavage of the ether bonds in the oxabicydic framework has been developed into a useful strategy to generate highly-substituted cyclohexyl derivatives from oxabicyclo [2.2.1] systems. This is an attractive approach because the facial bias inherent to the oxabicydic substrate can be exploited to control the stereochemistry before ring opening is induced. 

Functionalized medium-sized carbocyclic rings (especially seven- and eight-membered rings) can be accessed by this route through the use of the appropriate [3.2.1], [3.3.1], or [4.2.1] oxabicydic substrates. This approach avoids otherwise entropically disfavored cyclization approaches to these rings, and therefore has proven particularly valuable for the syntheses of certain families of natural products. 

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Abstract This chapter covers one of the most important areas of Ru-catalysed oxidative chemistry. First, alkene oxidations are covered in which the double bond is not cleaved (3.1) epoxidation, cis-dihydroxylation, ketohydroxylation and miscellaneous non-cleavage reactions follow. The second section (3.2) concerns reactions in which C=C bond cleavage does occur (oxidation of alkenes to aldehydes, ketones or carboxylic acids), followed by a short survey of other alkene cleavage oxidations. Section 3.3 covers arene oxidations, and finally, in section 3.4, the corresponding topics for aUcyne oxidations are considered, most being cleavage reactions. 

The 13 chapters of this book survey a range of fields of organic syntheses promoted by ruthenium catalysts, which involve hydrogenation, oxidation, various carbon-carbon bond formations, C-H activation, carbonylation, isomerization, bond-cleavage reaction, metathesis reaction, and miscellaneous nucleophilic and electrophilic reactions. 

Several selective cleavage reactions (classed as miscellaneous reactions in the introduction to this section) have been described. Thus, preferential 0-deacetylation of a phenyl acetate in the presence of an alkyl acetate occurred when 3-(4-acetoxy-3-methoxyphenyl)propylacetate was allowed to stand in pyrrolidine (or pyrrolidine in dichloromethane) at ambient temperature for 3 mins, followed by acidic quenching, to give 3-(3-methoxy-4-hydroxy)propylacetate in more than 80% yield (ref. 88). 

Photochemical elimination reactions include all those photoinduced reactions resulting in the loss of one or more fragments from the excited molecule. Loss of carbon monoxide from type I or a-cleavage of carbonyl compounds has been previously considered in Chapter 3. Other types of photoeliminations, to be discussed here, include loss of molecular nitrogen from azo, diazo, and azido compounds, loss of nitric oxide from organic nitrites, and loss of sulfur dioxide and other miscellaneous species. 

A few other miscellaneous reactions may be noted. Vinylsilicon-metal compounds in entries 4 and 30 undergo addition of HBr in an anti-Markownikoff sense to give 2-bromoethyl derivatives in some other related systems, HBr induces cleavage (see Section III,B,2). Also, the phenyl group in a phenyl-silicon-metal compound can undergo hexahapto interaction with a Cr(CO)3 group (entry 39). 

Miscellaneous Rearrangements and Bond Fission Processes - Chan and Arnold have carried out calculations to confirm that the two electrons in the biscation (145) are delocalized three-dimensionally. A review has given details of specific photoreactions of acyclic and cyclic saturated hydrocarbons that can provide paths for their functionalization. A study of the SET-induced photochemical bond fission processes in the series of 2-alkoxyphenylethers (146), (147) and (148) has been studied. The reaction involves bond cleavage in the inter-... 

A catalyst system159 consisting of a mixture of boron trifluoride, acetic acid and pyridine gives rapid and reproducible total hydroxyl analysis (silanol plus water) in a variety of silicone materials. This method avoids many of the interferences, empirical calibration and miscellaneous problems such as poor solubility, incomplete reaction and interfering siloxane cleavage associated with many earlier methods. Results obtained by this procedure compare well with results obtained by the lithium aluminium hydride procedure160. 

Miscellaneous Reactions. P Mn02 has also been used to perform various oxidation reactions the oxidative cleavage of... 

Miscellaneous Reactions. 2,4,6,8-Tetraethenyl-2,4,6,8-tetra-methylcyclotetrasiloxane acts as a chelating ligand for a bimetallic nickel(O) complex, similar to Karstedt s catalyst. The combination of and tetramethylcyclotetrasiloxane in the presence of Karstedt s catalyst cross-links the two tetramers to prepare a platinum-containing glass.Additionally, Bennetau and Boileau have functionalized with CgFnI under ultrasonic irradiation conditions to provide tetra(perfluorooctyl)-substituted D4 after reductive cleavage of the iodide with tributyltin hydride. ... 

This chapter collects miscellaneous examples of C-C bond cleavage by means of transition metal complexes. Although C-C bonds are generally stable under classical reaction conditions, progress in transition metal catalysis has rendered it possible to cleave various C-C bonds. Further investigation of the reaction mechanism and the development of new reaction is keenly awaited. 

Miscellaneous. a-Organylthioketones and esters can be prepared by treatment of enolates with RSSR (compare ref. 202), pyrolysis then giving a/S-unsaturated carbonyl compounds. If the same reaction is applied to cyclobutanones, and conditions chosen such that bis-sulphenylation and ring cleavage occur, a convenient route to thioacetals of y-ketoesters is obtained (Scheme 32). ... 

Miscellaneous Cycloadditions. The major reaction of alkyl- and aryl-substituted cyclopropenones with enamines to give amides involves formal C-1—C-2 bond cleavage of the cyclopropenone with cycloaddition to the enamine to give an initial dipolar intermediate (430). This mechanism also accounts for minor products. Work was extended to include reactions of enamines with diphenylcyclopropenethione and a re-evaluation of earlier evidence concerning reactions of diphenylcyclopropen-one and -thione with keten acetals. ... 

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