Epoxide formation and Ring-opening

Elaboration of 248 to 257 is depicted in Scheme 32. Acidic deketalization, basic epoxide formation, and silylation of the remaining hydroxyl group led to 249, which was subjected to ring opening with lithium dimethylcuprate in a regioselective (78 15) fashion to provide the desired alcohol 250 as the major... 

Epoxide formation and hydrolytic B-ring opening Penicillium notatum)... 

It is clear that the reaction conditions used in this study do not allow formation of polyglycoses from (28). The facility of the 1,2-epoxide formation and of the subsequent ring-opening do suggest, however, that different reaction conditions should permit ready synthesis of higher oligo-... 

The dihydroxylation of terminal ro-fluoroalkenes is accomplished by a mixture of hydrogen peroxide and formic acid. The first step is obviously the formation of an epoxide followed by ring opening.88 The reactivity of the C = C bond is very probably not affected by the distant C-F bond.88... 

As was illustrated in the first survey, all known halogenated terrestrial diterpenes are chlorohydrins (1), and that continues to be mainly the case. Obviously, one must be alert to the possibility of artifact formation from ring opening of the corresponding epoxide during isolation. Many nonhalogenated terrestrial diterpenoids also continue to be isolated (622). 

Until now, three main F-C transformations have been used for catalytic stereoselective formation of benzylic carbon stereocenters - 1,2-addition of arenes to carbonyl (C=X, X O, NR) moieties, 1,4-addition of arenes to electron-deficient C-C double bonds, and ring-opening reaction of epoxides. 

The use of the optically active (camphorylsulphonyl)oxaziridine did not afford enantioselectivity. A possible explanation for this lack of stereocontrol lies in the mechanism proposed (Scheme 56). It involves formation of an a-amino epoxide, its nucleophilic ring opening and either loss of a proton (route a) or hydrolysis (route b) (Scheme 56). 

This electrophilic attack likely occurred primarily at the epoxide, followed by ring opening of the homoallylic epoxide and formation of a cyclopropylmethyl cation which finally underwent transannular 7r-cylization. 

Racemic epoxide 40 was first transformed into p-dimethylamino alcohol 41 by nucleophilic epoxide ring opening. Treatment of this racemic mixture (1.0 mol equiv.) with ( + )-DIPT (1.2 mol equiv.),Ti(OPr-i)4 (2.0 mol equiv.), and t-BuOOH (0.6 mol equiv.) allowed to obtain N-oxide 42 and to recover the unreacted (,S)-enantiomer of 41 in 56% yield and 92% e.e. Standard manipulations of this material including /V-methylation, epoxide formation, and addition of isopropylamine, gave ( )-43. 

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