Epoxidation nucleophilic opening

Chiral A-amidino-l,2,3,4-tetrahydropyridines undergo a stereoselective epoxidation-nucleophilic opening sequence with either alcohols or organozinc reagents to give 2,3,6-trisubstituted piperidines where the relationship between the 2- and 3-positions is cis (Equation 15) <2005OL2747>. 

The experimental observations combine with the principles of nucleophilic substi tution to give the picture of epoxide ring opening shown m Figure 16 5 The nucleophile attacks the less crowded carbon from the side opposite the carbon-oxygen bond Bond... 

Nucleophilic ring opening of epoxides by ammonia (Section 16 12) The strained ring of an epoxide is opened on nucleo philic attack by ammonia and amines to give 3 ammo alcohols Azide ion also re acts with epoxides the products are p azido alcohols... 

Primary cycloaUphatic amines react with phosgene to form isocyanates. Reaction of isocyanates with primary and secondary amines forms ureas. Dehydration of ureas or dehydrosulfuri2ation of thioureas results in carhodiimides. The nucleophilicity that deterrnines rapid amine reactivity with acid chlorides and isocyanates also promotes epoxide ring opening to form hydroxyalkyl- and dihydroxyalkylaniines. Michael addition to acrylonitrile yields stable cyanoethylcycloalkylarnines. 

Nucleophilic opening of oxiranes to give ultimately 1,2-diols is usually effected without isolation of the oxirane oxiranation (epoxidation) of alkenes with unbuffered peroxy-ethanoic acid or hydrogen peroxide in methanoic acid (Section 5.05.4.2.2(/)) tends to give monoesters of 1,2-diols (e.g. 53), which can be hydrolyzed to the diols (Scheme 46). 

Steps 1-2 of Figure 27.14 Epoxide Opening and Initial Cyclizations Cyclization is initiated in step 1 by protonation of the epoxide ring by an aspartic acid residue in the enzyme. Nucleophilic opening of the protonated epoxide by the nearby 5,10 double bond (steroid numbering Section 27.6) then yields a tertiary carbo-cation at CIO. Further addition of CIO to the 8,9 double bond in step 2 next gives a bicyclic tertiary cation at C8. 

Posner recently reported a very simple and fast way to activate epoxides towards nucleophilic opening by ketone lithium enolate anions by use of BF3 Et20 (1 equiv.) [73]. The application of this procedure to the nucleophilic opening of propene oxide with the lithium enolate of 2-cycloheptanone, obtained by the conjugate addition of trimethylstannyllithium to 2-cycloheptenone, afforded the stan-... 

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... 

Cir—R S Nucleophilic substitution, conjugate addition and epoxide ring-opening h... 

The following is an example for a sequential one-pot epoxide formation/nucleophilic opening process using (S)-4-(benzyloxy)-l,2-butanediol, iV-(p-tohienesulfonyl)-imida-zole, and 2-lithio-l,3-dithiane ... 

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

One of the most well used methods for the synthesis of aziridines involves a two (or sometimes more) step process in which an epoxide is opened by a nitrogen nucleophile. The resulting P-amino alcohol (e.g. 79) is then converted to an aziridine via a number of different processes. This method is generally not broadly applicable when a variety of different groups on the nitrogen of the aziridine are desired. A useful method to convert an epoxide to a number of different /V-sulfonyl aziridines (e.g. 80) has been reported <06S425>. Simple addition of a sulfonamide to an epoxide provides high yields of 79 which is readily closed to form the aziridine. 

Stereocontrolled nucleophilic opening at the C 1-position of epoxides to furnish substituted piperidine 182 was accomplished through the use of Lewis acids TMSOTf or Sc(OTf), <06CC2156>. 

Functional groups were selectively introduced at the C-2 position of isophorone by epoxide ring-opening by several nucleophiles with active methylene groups. Different behavior was observed depending on the reaction conditions and the nature of the nucleophilic agents [57]. The best experimental systems involved PTC or KF-alumina under solvent-free conditions and MW irradiation (Eq. 37 and Tab. 5.15). 

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