Exocyclic position

Various terminal allylic compounds are converted into l-alkenes at room temperature[362]. Regioselective hydrogenolysis with formate is used for the formation of an exo-methylene group from cyclic allylic compounds by the formal anti thermodynamic isomerization of internal double bonds to the exocyclic position[380]. Selective conversion of myrtenyl formate (579) into /9-pinene is an example. The allylic sulfone 580 and the allylic nitro compound... 

The difference of reactivity between 2,4-dinitrochlorobenzene and the iron complexes is explained by the fact that the additional electronic density is localized on the oxygen atoms in P-exocyclic position in the case of the nitro derivatives and on the ring in the case of the iron complexes [91]. 

The dimerization in exocyclic positions was considered. For the C-C a bond energy, we employed the value 82.17 kcal/mole for (3 unit, we used the value 15.8 kcal/mole obtained from the correlation of experimental and HMO delocalization energies. 

This method provides a convenient synthesis of alkenes with the double bond in a relatively unstable position. Thus reduction of the p-toluenesulfonylhydrazones of a,(3-unsaturated aryl ketones and conjugated dienones gives rise to nonconjugated olefins. Unsaturated ketones with endocyclic double bonds produce olefins with double bonds in the exocyclic position. The reduction of p-toluenesulfonylhydrazones of conjugated alkynones furnishes a simple synthesis of 1,3-disubstituted allenes. ... 

Evidently, these or closely related intermediates are accessible and reactive, since the synthesis was successfully achieved as outlined in Scheme 13.28. In addition to the key cationic cyclization in Step D, interesting transformations were carried out in Step E, where a bridgehead tertiary alcohol was reductively removed, and in Step F, where a methylene group, which was eventually reintroduced, had to be removed. The endocyclic double bond, which is strained because of its bridgehead location, was isomerized to the exocyclic position and then cleaved with Ru04/I04. The enolate of the ketone was then used to introduce the C(12) methyl group in Steps F-3 and F-4. 

Reactions at the exocyclic position of cyclophosphazene derivatives represent a means for widely expanding the range of available phosphazenes. The synthesis of covalently bound cyclophosphazene heme complexes starts with N3P3 (OPh), -Cl which is converted to N3P3(OPh)5NMeCH2CH2CN. Following reduction of the... 

Stable heptafulvenes (53) with strong acceptor groups in the exocyclic position... 

Nitrogen-15 NMR has been used to study the course of acylation and carbamidization reactions of 3-amino-5-methylthio-1,2,4-thiadiazole (3). Using a N label in the 2-position of (3), its reaction with hard nucleophiles was found to proceed via initial reactioa on the 2-position followed by a Dimroth rearrangement to give the acylated product (4) with the N label in the exocyclic position. The reaction of (3) with soft nucleophiles, such as methyl isocyanate occurs directly on the exocyclic nitrogen to give the urea (5) (Scheme 1) <84CHEC-l(6)463 >. 

Extending their earlier work on Vilsmeier formylation (c/. Vol. 7, p. 36), Traas et al. have formylated the a/S-unsaturated ketone isophorone almost exclusively at the more favoured exocyclic position to yield (190), which may be selectively... 

The reaction generally tolerates steric hindrance at the 2-exocyclic position as well as at the 4- and 5-positions. However, the reaction rate was found to be sensitive to steric effects. Thus, thiolysis of a threonine-derived oxazohne 332 was considerably slower than that for the corresponding serine-derived oxazoline 333 (Scheme 8.101). The rate difference could be exploited to selectively convert a serine-derived oxazoline to a thioamide in the presence of a threonine-derived oxazoline. 

The most recent procedure to be adopted165 employs the essentials of Scheme 12 but differs simply in the nature of the carbonyl compound employed aldehydes and ketones are replaced by acid chlorides or acid cyanides. At the time of writing this procedure has been applied to the naphthalene series only to give 96 containing alkyl, electron-donating and electron-withdrawing groups at the exocyclic position (Scheme 13). The specific... 

Like ylides, bis-methylene-phosphoranes can also be built into 7i-systems in different ways (see Scheme 6), with one of the P=E bonds in an exocyclic position, or with the entire 3c-4e 7i-system incorporated into the cyclic delocalization. 

The Pd(0)-catalyzed allylation of 96 with acrolein dimethyl acetal gives exclusively compound 104. The 7j3-allylpalladium cationic complex (4, R = OMe) is attacked only at the center bearing the substituent MeO (80SC147), thus emphasizing the importance not only of steric effects in the electrophile but also of the electronic effects in the Tsuji-Trost reaction (92T1695). Indole 96 has been also allylated with epoxide 105 under Pd(0) catalysis by Trost and Molander (81JA5969). The intermediate cationic complex is attacked at the exocyclic position, 106 being formed, as shown in Scheme 22. 

The double bond is kept in the exocyclic position by conjugation with the carbonyl group (the free base absorbs at 3270 cm-1). The free base of l-(a-picolyl)-6,7-methylenedioxy-3,4-dihydroisoquinoline also possesses the stabilized enamine structure, whereas the imino structure is exhibited by the 1-methyl analog, as shown by comparison of the... 

Dolbier and Dai 43> found through intramolecular competition experiments with 1,1-dideuterioallene and acrylonitrile at 206—225 °C that the carbon bearing deuterium atoms was found predominantly at the exocyclic position. The observed product ratio, interpreted in terms of a partitioning of an intermediate, gave Ah/ d 1.13—1.21. 

The boat and the chair forms of cyclohexane show only equatorial and axial exocyclic positions. In contrast, the twist conformers display pseudoequatorial e pseudoaxial (a ) and isoclinal (i) positions [102]. 

The preparation of fluorinated carbohydrates via nucleophilic displacement of the sulfonate group of the corresponding sulfonates by fluoride is a well-known reaction 24-27 however, potassium fluoride, which was used to prepare the first alkyl fluoride type of sugar derivative,28 has been progressively replaced by the alkylamine fluorides (see Section 1.1.4.2.1.2.). The substitution of relatively unhindered primary mesylates or tosylates in exocyclic positions of carbo-... 

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