Rearrangement, and addition

Schematically, the two major types of reactions undergone by epoxides are rearrangements and addition of nucleophiles. Rearrangements can lead to toxic intermediates, precursors, or metabolites, whereas nucleophilic additions can lead to alkylation of biomacromolecules, i.e., formation of covalent adducts.

When coordinated to the metal in the rf form heteroaidehyde ligands react readily with electrophiles. As expected, carbon electrophiles add to the chalcogen atom. Very likely, the site of the initial attack of protons is also the chalcogen atom. However, rapid succeeding rearrangement and addition of an anion usually lead to chalcogenolato complexes. 

Type I Asymmetric Acyl Addition to 7r-Nucleophiles Steglich and Related Rearrangements and Additions to Silyl Ketene Acetals/lmines... 

The [2+2] cycloaddition of benzyne 61 to substituted thiophenes (Equation 3) is a general method to trap such reactive intermediates. Usually, the adducts 62 are postulated rearrangement and addition of a second equivalent of benzyne gives 1- and/or 2-substituted naphthyl sulfides 63 <2003JOC70, 2005JP0477>. 

Neale, R. S. Nitrogen radicals as synthesis intermediates. N-Haloamide rearrangements and additions to unsaturated hydrocarbons. Synthes/s 1971, 1-15. 

For steric reasons, (E)-alkenes (and transition states leading to ( )-alkenes) are usually lower in energy than (Z)-alkenes (and the transition state leading to them) because the substituents can get farther apart from one another. A reaction that can choose what it forms is therefore likely to favor the formation of ( )-alkenes. For alkenes formed by El elimination, this is exacdy what happens the less hindered ( )-alkene is favored. Carbocations can also lead to two other pathways, which do not yield to stable products but, instead, to other carbocations, that is, rearrangement and addition to an unsaturated linkage, for which the whole spectrum of reaction types is stiU open. 

In the steroid series, o-ring enlargement accompanies reaction of a secondary alcohol with PBrs (eq 7.) It should be noted that reaction of Phosphorus(V) Chloride with this same substrate gave direct replacement of the OH with Cl with inversion of configuration. Rearrangement and addition of bromine across a double bond has been noted in the reaction with a propargyl alcohol derivative (eq 3). ... 

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