Hydrogen iodide with epoxides

The catalyst system of TOP18 and TOT is remarkably stable and long-lived if the reaction system is kept free of water and air. Contamination of the reaction mixture with water will lead to TOT decomposition (17). This reaction produces hydrogen iodide which reacts with epoxide 1. Air is deleterious to both catalyst components. Introduction of air into the process can cause oxidation of iodide anion to iodine which will dealkylate TOT. These reactions lead to loss of iodine value from the catalyst system which is monitored by XRF during production. 

When the phenyl substituent is one carbon removed from the epoxide ring, as in 2,3-opcxy-l-phenylpropaue, nucloophiiic attack can evidently occur at either possible reaction sites, since a mixture of iodohydrins (Eq. 714) la obtained on treatment with hydrogen iodide.1 7... 

The addition of iodine azide to primary allylic alcohols occurred with complete regio- and simple diastereoselectivity allowing the direct preparation of valuable 3-azido-1,2-epoxides, e.g., 12 and 13, by base-promoted elimination of hydrogen iodide from the intermediate 3-azido-2-iodo alcohols44. 

Electrophilic Addition.—5a -Cholest-2-ene (67), on reaction with iodine, potassium iodate, and sulphuric acid in aqueous dioxan, gave the 2/3,3a-diol (69) as the main product. " The intermediate 2,3-epoxide (68) can be isolated by using a modified procedure, with iodine in aqueous dioxan in the presence of silver oxide to trap liberated hydrogen iodide." The 2-methyl and 3-methyl derivatives of 5a-cholest-... 

The transformation of oxaspirohexanes to cyclopentanones can be achieved with lithium iodide in refluxing dicbloromethane > (Schemes 96, 97a, b). This isomerisation, first described by Leriverend and used by Trost in a modified version, was previously reported for oxaspirohexanes bearing two hydrogens on the epoxide ring. It was later found in our laboratory that it even works... 

Both epoxides and aromatic ketones have been shown to be iodinated reductively with tetramethyldisiloxane-iodine to the corresponding benzyl iodides in good yields.Allylic acetals will undergo reaction with trimethylsilyl chloride-sodium halide to produce B-iodoacetals on work-up in a sequence equivalent to overall conjugate addition of hydrogen iodide. 

Epoxidation of ot.fl-unsaturated ketones by hydrogen peroxide or /-butyl peroxide is promoted by the addition of tetra-n-butylammonium fluoride [10], whereas the corresponding reaction with 1,4-disubstituted but-2-en-l,4-diones is catalysed by quaternary ammonium iodides [11], Oxiranes are also produced by the catalysed reaction of /-butyl peroxide with a,f)-unsaturated sulphonates under basic conditions [12]. 

A structurally unusual 3-blocker that uses a second molecule of itself as the substituent on nitrogen is included here in spite of the ubiquity of this class of compounds. Exhaustive hydrogenation of the chromone (13-1) leads to a reduction of both the double bond and the carbonyl group, as in the case of (11-2). The car-boxyhc acid is then reduced to an aldehyde (13-2) by means of diisobutylaluminum hydride. Reaction of that intermediate with the ylide from trimethylsulfonium iodide gives the oxirane (13-3) via the addition-displacement process discussed earlier (see Chapters 3 and 8). Treatment of an excess of that epoxide with benzylamine leads to the addition of two equivalents of that compound with each basic nitrogen (13-4). The product is then debenzylated by catalytic reduction over palladium to afford nebivolol (13-5) [16]. The presence of four chiral centers in the product predicts the existence of 16 chiral pairs. 

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