Alcohols epoxide ring-opening

Epoxide ring-opening witli transfer of an sp carbon moiety was applied in a sbori syntliesis [44] of eicosanoid 56 [45], relevant in marine prostanoid biosyn-tliesis (Scheme 9.13). Honioallyl alcohol 55 was obtained in good yield from 54 by use of a cyano-G dman alketiylciiprate [46]. 

Ethylene oxide is a highly active intermediate. It reacts with all compounds that have a labile hydrogen such as water, alcohols, organic acids, and amines. The epoxide ring opens, and a new compound with a hydroxyethyl group is produced. The addition of a hydroxyethyl group increases the water solubility of the resulting compound. Eurther reaction of ethylene oxide produces polyethylene oxide derivatives with increased water solubility. 

An interesting alcoholysis of epoxides has been reported by Masaki and coworkers <96BCSJ195>, who examined the behavior of epoxides in the presence of a catalytic amount of the Tt-acid tetracyanoethylene (TCNE, 85) in alcoholic media. Ring-opening is very facile under these conditions, typically proceeding via normal C-2 attack, as exemplified by styrene oxide (86). Certain epoxy ethers (e.g., 89) undergo C-1 attack due to anchimeric assistance. Analysis of the reaction mixtures revealed the presence of captodative ethylenes (e.g., 85) formed in situ, whieh were shown to be aetive in eatalyzing the reaction. The proposed mode of catalysis is represented by the intermediate 87. The affinity of these captodative olefins for... 

Scheme 7.4 illustrates some of the important synthetic reactions in which organolithium reagents act as nucleophiles. The range of reactions includes S/v2-(ype alkylation (Entries 1 to 3), epoxide ring opening (Entry 4), and formation of alcohols by additions to aldehydes and ketones (Entries 5 to 10). Note that in Entry 2, alkylation takes place mainly at the 7-carbon of the allylic system. The ratio favoring 7-alkylation... 

Acid catalysis assists epoxide ring opening by providing a better leaving group (an alcohol) at the carbon atom undergoing nucleophilic attack. 

An alternative disconnection of homopropargylic alcohols substrates for intramolecular hydrosilylation is the opening of an epoxide with an alkynyl anion. This strategy was employed in a total synthesis of the macrolide RK-397 (Scheme 20). Epoxide ring opening serves to establish homopropargylic alcohol C with the appropriate stereochemistry. A hydrosilylation/oxidation protocol affords the diol E after liberation of the terminal alkyne. The... 

Starting with a copper catalyzed epoxide ring opening, using phenyl magnesium chloride, a secondary alcohol was generated, which in turn was transformed into an electrophile by tosylation (Scheme 29). The tosylate 117... 

Aliphatic or aromatic alcohols can be alkylated by epoxides under either basic or acidic reaction conditions. Reaction of aliphatic alcoholates with epoxides can be complicated by base-induced rearrangement or oligomerization of the epoxide, because alcoholates are strongly basic and because the product of epoxide ring opening is again an alcoholate. These side reactions can be suppressed by using only catalytic amounts of base (Scheme 4.78). The examples sketched in Scheme 4.78 show that under basic reaction conditions nudeophilic attack occurs preferentially at the sterically most accessible carbon atom. 

Ergiiden, J.-K. Schaumann, E. Phosphoryl functionalized bishomoallyl alcohols by ring opening of epoxides with lithiated allyldiphe-nylphosphane oxide. Synthesis 1996, 707—710. 

The alcohol or glycol then acts as a nucleophile in an Sn2 displacement, which occurs quite easily because the epoxide ring opens in the process, thus relieving the strain associated with the small ring ... 

With good nucleophiles, under relatively mild conditions, 2,3-epoxy alcohols will undergo epoxide ring opening at C-2 or C-3. In simple cases, nucleophilic attack at C-3 is the preferred mode of reaction. However, as the steric congestion at C-3 is increased, or if substituents play a significant electronic role, attack at C-2 can predominate.86... 

Controlled cA-dihydroxylation of the olefinic double bond of alcohol 141 allowed preparation of 5a-carba-a-D-glucopyranose (142), whilst 5a-carba-a-D-mannopyranose (146) and 5a-carba-P-D-glucopyranose (147) were prepared through epoxidation, ring opening, and final deprotection. Unfortunately, an attempt to obtain the P anomer of 146 by cis-... 

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