Endo position

The c/s-fused diaziridines (31a) and (31b) are also an equilibrium system, interchanging exo and endo positions of methyl and ethyl groups. The NMR spectrum shows two methyl peaks at 0 °C, coalescing to a single sharp peak at 75 °C. The ethyl group shows the sharp characteristic quartet-triplet splitting pattern at 75 °C (74JOC3187). 

The equilibrium situation for simple substituted 2-ulkenyl alkali metal derivatives can be estimated by a rule of thumb electron-accepting and electropositive substituents ( ) prefer the exo position, but electron-donating and electronegative substituents ( ), including alkyl groups, tend to occupy the endo position. With increasing steric demand of the substituent, the exoisomer becomes more favored. 

With AT. trichosporium 0B3b, epimerization with exo, exo, exo, exo-2,3,5,6-d4-norbornane upon hydroxylation occurs (83), which parallels results for cytochrome P-450 hydroxylation with this substrate (91). The extent of epimerization with MMO, however, was significantly lower, being 2% following hydrogen atom abstraction from the endo position compared to 18% with cytochrome P-450, and 5% after abstraction at the exo position as compared to 14% with cytochrome P-450... 

Extrapolation of the data to zero time suggests that the endo acetates (65) and (67) are produced in amounts as great as or greater than the exo isomer. Solvolysis studies of the bicyclo[3.1.0]hex-2-en-6-yl cation reveal that nucleophilic capture occurs preferentially from the exo side to give (66) rather than (67). Similarly, solvolysis of cation (63) leads to exo product (64) in at least a 90% yield. Photolysis of benzene in deuteriophosphoric acid results in (68), in which all the deuterium is incorporated into the 6-endo position ... 

The most studied of the water-soluble metallophthalocyanines (Zn, Al, Ga) are the sulfonic acids. These are prepared by cyclotetramerization of 4-sulfophthalic acid or its derivatives (Figure 6),246,247 or by the direct sulfonation (oleum) of the metallophthalocyanine.248 The latter method gives complex mixtures, since direct sulfonation occurs at both exo and endo positions. These mixtures may be separated by chromatographic methods (usually reverse-phase HPLC). Thus... 

A series of zinc(II) phthalocyanines with other sorts of solubilizing groups in exo or endo positions (carboxyalkyl, carboxyalkoxy, amino acid) has been synthesized and subjected to preliminary in vitro assays.257 Interestingly, the seryl derivative zinc(II) 2,9,16,23-tetrakis(l-car-boxy-2-hydroxyethylaminocarbonyl)phthalocyanine proved to be cytotoxic (i.e., toxic in the dark) which is not so commonly observed with macrocyclic systems. 

The oxidative addition of one equivalent of X2 (X=C1, F) to S4N4 under mild conditions produces 1,5-S4N4X2.106 The structure of 1,5-S4N4C12 (32) consists of a folded eight-membered ring [d(S- -S) = 2.45 A] with the exocyclic substituents in exo,endo positions. The reaction of 32 with (Me3SiN)2S is the best route to the binary sulfur nitride S5N6 (11).42... 

The treatment of 23 with methyllithium in the presence of furan gave rise to the tetracyclic product 26, which is obviously a [4 + 2]-cycloadduct of furan to the 1,2-cyclopentadiene derivative 25 [27]. The feature that the oxanorbornene system of 26 carries its saturated substituent in the endo-position is analogous to the [4 + 2]-cycloadducts of furan to all six-membered cyclic allenes (see Section 6.3). Balci et al. [36] also provided evidence for the generation of l-phenyl-l,2-cyclopentadiene. They postulated this species to be an intermediate in the reaction of l-phenyl-2-iodocydo-pentene with potassium tert-butoxide in benzene at 240 °C, which resulted in the formation of 1-phenyl- and 1,2-diphenylcyclopentene. Both products were considered as evidence in favor of the diradical nature rather than the allene structure of 1-phe-nyl-1,2 -cyclopentadiene. 

Dimethyl isomannide (VII) has both methoxy groups in endo-position and might even have better complexation than dimethyl isosorbide (as discussed above for isomannide). However, it does not have optical activity. 

Polynitro derivatives of pentacyclo[5.4.0.0 .0 °.0 ]undecane have attracted interest as potential high-energy explosives. Molecular strain in this caged system could arise from both the constrained norbomyl moiety and the cyclobutane ring. Additional strain would be expected from nonbonding interactions if the S-endo and 1 l-endo positions were substituted with gm-dinitro groups. 

Due to the low reactivity of the nitrogen, incorporation of the pyroglutamic acid into endo-positions by stepwise chain elongation is difficult (see reft49 and refs cited therein). It may be achieved using suitably protected aminoacyl-pyroglutamic acid derivatives as dipeptide synthons. These are accessible in satisfactory yields, e.g. by acylation of pGlu-OBzl with N-protected amino acid pentafluorophenyl esters in the presence of NaH or LiHMDS. 49 ... 

The stereochemistry with respect to the ketene iminium salt in cases of monosubstituted or unsymmetrically disubstituted derivatives in cycloadditions to alkenes show differences from the ketene counterpart. In contrast to ketene cycloadditions of monosubstituted ketenes with alkenes where the substituent in the bicyclic derivative ends up in the endo position, the cycloaddition of two monosubstituted ketene iminium salts with cyclopentene and cyclohexenc gives the e.wp-substituted derivatives 4.6... 

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