Stereospecific ring opening

Halogen atoms can be stereoselectively introduced by ring-opening of y-azir-idinyl-a,P-enoates (Scheme 2.39). Treatment of 149 with diethylaminosulfur tri-fluoride (DAST) results in stereospecific ring-opening to yield fluorinated derivative 150 [59]. A related stereoselective conversion of y-aziridinyl-a,P-enoates 151 into allyl halides 152 by use of lithium halide in the presence of Amberlyst 15 was also reported recently [60]. 

Similarly, the stereospecific formation of cis-2-butene from cis-2,3-dimethylthiirane dioxide19 may be rationalized in terms of a stereospecific ring opening to give the threo-sulfinate 120 which, in turn, decomposes stereospecifically to yield the cis-alkene, hydroxide ion and sulfur dioxide73. The parent thiirane dioxide fragments analogously to ethylene, hydroxide ion and sulfur dioxide (equation 49). 

Scheme 36 Stereospecific ring opening reaction of thione 122a with sodium ethoxide...

Equation (4) shows a stereospecific ring opening of 77 to give allylic alcohol 78 in excellent yield <2001JA8851, 2002JA3939>. 

The synthesis in Scheme 13.40 uses stereospecific ring opening of the epoxide to establish the stereochemistry of the C-4 methyl group. The starting material can be made by enantiospecific epoxidation of the corresponding allylic alcohol.137... 

The mechanism of the aminolysis and the electronic effects of substituents at C-2 or C-4 on the kinetics of amide bond formation have been studied. In some cases, ring opening with amines occurs with partial isomerization of the exocyclic double bond. However, with more hindered compounds, such as unsaturated oxazolones derived from ketones, ring opening is stereospecific.Ring opening using diamines has also been described. Selected examples of dehydroamino acid amides prepared by aminolysis of unsaturated 5(4//)-oxazolones are shown in Table 7.40 (Fig. 7.51). 

For amides obtained by stereospecific ring opening of (Z)- and ( )-2-phenyl-4-(a-phenylethylidene)-5(477)-oxazolone 505 and 508, cyclization gives the imida-zolone 510 or 4-methyl-l-phenyl-3-isoquinolinecarboxylic acid anilide 507. The products are determined by the double-bond geometry in the starting material and by the experimental conditions (Scheme 7.161). ... 

It has been shown that the syn-tricyclooctadiene iron carbonyl complex 58 [Eq. (4)] readily undergoes stereospecific ring opening to afford the exo-bicyclooctatriene complex 59, and the anfi-tricyclooctadiene iron carbonyl... 

Give the structure and stereochemical designation of all possible cycloolefin polymers that might, in principle, be obtained by stereospecific ring-opening metathesis polymerisation. 

C to —10°C) followed by a Dess-Martin oxidation provided the necessary azidoaldehyde. An intramolecular Staudinger cyclization followed by reduction of the resultant amine provided azepine 364. Treatment of 364 with iodine induced an interesting double cyclization. Initial iodination of the double bond is followed by aziridinium ion formation 365. An intramolecular and stereospecific ring opening by the carboxylate provides the target (—)-stemospironine. 

As discussed briefly in Section II,A, dimethy l-(p-methoxyphenyl)aziridine-2,3-dicarboxylate (6) undergoes a stereospecific ring opening generating ester-... 

The stereospecific ring-opening reactions of cyclopropyl derivatives have played a key role in establishing selection rules for pericyclic processes . Extensive and conclusive evidence has been presented in support of DePuy s initial postulation that disrotatory ringopening and C-X bond heterolysis are synchronous processes, and all kinetic , stereochemical and theoretical findings lend credence to the DePuy-Hoffmann-Wood ward rule Substituents on the same side of the 3-membered ring as... 

Alkenylgermanes have been synthesized highly stereoselectively by addition of triethylgermyl lithium to cyclobutyl ketones and subsequent Lewis acid-promoted stereospecific ring opening of the resulting cyclobutylethanol derivatives (Scheme 11.43) [67]. 

Y. Niibo, T. Nakata, J. Otera, H. Nozaki, Stereospecific ring opening at the benzylic carbon of phenyloxirane derivatives by alcohols, Synlett (1991) 97. 

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