Selective bond cleavage mechanism

Remarkable solvent effects on the selective bond cleavage are observed in the reductive elimination of cis-stilbene episulfone by complex metal hydrides. When diethyl ether or [bis(2-methoxyethyl)]ether is used as the solvent, dibenzyl sulfone is formed along with cis-stilbene. However, no dibenzyl sulfone is produced when cis-stilbene episulfone is treated with lithium aluminum hydride in tetrahydrofuran at room temperature (equation 42). Elimination of phenylsulfonyl group by tri-n-butyltin hydride proceeds by a radical chain mechanism (equations 43 and 44). 

Mechanism Selective bond cleavage. Cationic polymerization of... 

Toutchkine, A. and Clennan, E.L. (2000). A new mechanism for oxidative C-S bond cleavage during reactions of singlet oxygen with organic sulfides electronically dictated reaction selectivity in the persulfoxide intermediate. J. Am. Chem. Soc. 122, 1834-1835... 

The Mn + complexed ions appear to be the most selective and efficient initiator system for grafting to polysaccharides so far described. The mechanism of the initiation reaction has been studied in our laboratories by model experiments and ESR spectroscopy. There are two possible reactions indicated. Bond cleavage of a vicinal diol according to reaction (22) is one possibility. Another and faster reaction with Mn3+ giving radicals appears to be oxidation of aldehyde groups (24) to alkoxy radicals ... 

The C-H/olefin coupling of aryloxazolines proceeds with unusual product selectivity. In this case, alkylation products, i.e., formally dehydrogenation products, are obtained as a major product (Eq. 22) [11]. These types of dehydrogenation compounds are believed to be formed via a carbometalation pathway. The first example of this type of alkenylation of arenes with olefins using palladium(II) complexes via C-H bond cleavage was reported in 1967 [32]. Later, several efforts were made to perform this reaction in a catalytic manner [33]. In 2001, Milstein et al. [34] reported the oxidative alkenylation of arenes with olefins using a Ru/02/C0 catalyst system (Eq. 23). Details of the reaction mechanism have not been elucidated. 

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