Addition epoxidation

AH of the amine hydrogens are replaced when MDA or PMDA reacts with epoxides to form amine based polyols. These polyols can be used in reactions with isocyanates to form urethanes or with additional epoxide to form cross-linked thermo set resins. 

A concerted [2 + 2] cycloaddition pathway in which an oxametallocycle intermediate is generated upon reaction of the substrate olefin with the Mn(V)oxo salen complex 8 has also been proposed (Scheme 1.4.5). Indeed, early computational calculations coupled with initial results from radical clock experiments supported the notion.More recently, however, experimental and computational evidence dismissing the oxametallocycle as a viable intermediate have emerged. In addition, epoxidation of highly substituted olefins in the presence of an axial ligand would require a seven-coordinate Mn(salen) intermediate, which, in turn, would incur severe steric interactions. " The presence of an oxametallocycle intermediate would also require an extra bond breaking and bond making step to rationalize the observation of trans-epoxides from dy-olefms (Scheme 1.4.5). 

I The order of topics remains basically the same but has been changed to devote Chapter 3 entirely to alkanes and Chapter 4 to cycloalkanes. In addition, epoxides are now introduced in Chapter 7 on alkenes, and coverage of heterocyclic chemistry has been moved to Chapter 24. 

Scheme 2.36. Synthesis of bicycloillicinone aldehyde (2-158) by a domino Michael addition/epoxide opening.

To date, the most frequently used ligand for combinatorial approaches to catalyst development have been imine-type ligands. From a synthetic point of view this is logical, since imines are readily accessible from the reaction of aldehydes with primary or secondary amines. Since there are large numbers of aldehydes and amines that are commercially available the synthesis of a variety of imine ligands with different electronic and steric properties is easily achieved. Additionally, catalysts based on imine ligands are useful in a number of different catalytic processes. Libraries of imine ligands have been used in catalysts of the Strecker reaction, the aza-Diels-Alder reaction, diethylzinc addition, epoxidation, carbene insertions, and alkene polymerizations. 

Partial ergot alkaloid substrates of 5 and related, conformationally fixed styrenes 6-8 have been found to undergo electrophilic additions (epoxidation, HOBr addition and... 

The reaction of 2-chloroisobutyrophenones and nitromethanide anion has stereose-lectively provided ( )-3-nitro allylic alcohols.58 The Gibbs free enthalpies of reaction in DMSO for carbanion addition, epoxide formation, and rearrangement to 3-nitro allylic alcohol, as elementary steps for the reaction, have been estimated from corresponding neutral gas reactions and using a thermodynamic approach to the transfer of gaseous compounds to DMSO. 

In addition, ethylene oxide is polymerized to polyethylene oxide. The terminal primary hydroxyl group of the substituent reacts with additional epoxide to form pendant oxyethylene chains ... 

Lithium organocuprates are reagents for cross-coupling, conjugate addition, epoxide opening, ketone synthesis and addition to acetylenes ... 

Trichothecene mycotoxins are a group of sesquiterpenoid mycotoxins produced by fungi from the Fusarium family. There are four types Type-B such as nivalenol differs from Type-A such as diacetoxyscirpenol by the presence of the keto-group in the C8 position. Type-C has an additional epoxide group, and Type-D are macrocyclic trichothecenes. Human and animal toxicoses by these toxins have been dne to the consnmption of contaminated grain. The structure of some of the Type-A and Type-B componnds is shown in Table 14.2. 

Unsaturated polymers undergo reactions such as isomerisation, cyclisation, addition, epoxidation and hydrogenation. Saturated polymeric hydrocarbons undergo substitution on the main chain or the side chain. Loaded butyl vulcanisates were shown to be less... 

The basic functional groups— products from the rubbers ozonolysis were identified and quantitatively characterized by means of IR-spectros-copy and H-NMR spectroscopy. The aldehyde—ozonide ratio was 11 89 and 27 73 for E-BR and BR, respectively. In addition, epoxide groups were detected, only in the case of BR, their yield was about 10 per cent of that of the aldehydes. On polyisoprenes the ozonide—ketone—aldehyde ratio was 40 37 23 and 42 39 19 for E-IR and Z-IR, respectively. Besides the already-specified functional groups, epoxide groups were also detected, their yields being 8 and 7 per cent for E-IR and Z-IR, respectively, with respect to reacted ozone. In the case of 1,4-rrara-polychloroprene, the chloroanhydride group was found to be the basic carbonyl product. 

Using W-CPBA/CH2CI2 as oxidative system, the epoxidation of silylated alcohols 202 gave the major a /i-epoxide anti-KXS) (Scheme 4.61). The dia-stereoselectivities of epoxide 203 showed a strong substrate-dependent stereochemical outcome. The anti syn ratio varied from 1.4 1 to 13 1 upon changing the R group. In addition, epoxidation of the unprotected alcohols furnished a lower dr than that of protected alcohol. 

There are some important features of reductive dioxygen activation which are apparent from Table II. The chemoselectivity between allylic oxidation and epoxidation is illustrated by the first two entries with no reducing additive epoxidation is strongly suppressed in favor of allylic oxidation to cyclohexenol and cyclohexenone when 0 is the... 

Macrolides are a class of valuable antibiotics which include a 16- or 14-membered macrolactone ring, generally at least one appended sugar unit, and, in most cases, additional epoxide and/or hydroxyl groups. These functional groups contribute to structural diversification and serve to improve the bioactivity profiles of natural products (Figure 3.96). 

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