Intramolecular interactions adducts

Photoinduced intramolecular interaction of t-S and tertiary amine moieties linked with a polymethylene chain has also been studied24. The photoexcitation of fraws-stilbene in which a tertiary amine is attached to the ortho position with a (CH2)i-3 linker leads to fluorescent exciplexes by intramolecular electron transfer, and results in no more than trans-cis isomerization. The failure to give adducts from the intramolecular exciplexes could arise from the unfavourable exciplex geometry to undergo the necessary bond formation. 

As pointed out before, the IR/UV double resonance spectra of the complexes between F and the enantiomers of 2-amino-1-propanol (alaninol) exhibit spectral features due to structures involving not only the expected intermolecular hydrogen bonding (either OH- - -O or OH- - -N), but also extensive intramolecular OH- - -N and OH- - -TThydrogen bonding. Similar intramolecular interactions are present in the isomeric [C/j-M/ r], [C/j-M/ s], and [C/j-Mss] adducts as well. 

The chiral dialuminum Lewis acid 14, which is effective as an asymmetric Diels-Alder catalyst, has been prepared from DIBAH and BINOL derivatives (Scheme 12.12). " The catalytic activity of 14 is significantly greater than that of monoaluminum reagents. The catalyst achieves high reactivity and selectivity by an intramolecular interaction of two aluminum Lewis acids. Similarly, the chiral trialuminum Lewis acid 15 is quantitatively formed from optically pure 3-(2,4,6-triisopropylphenyl)binaphthol (2 equiv) and MeaAl (3 equiv) in CH2CI2 at room temperature (Scheme 12.12). " The novel structure of 15 has been ascertained by NMR spectroscopic analysis and measurement of the methane gas evolved. Trinuclear aluminum catalyst 15 is effective for the Diels-Alder reaction of methacrolein with cyclopentadiene. Diels-Alder adducts have been obtained in 99% yield with 92% exo selectivity. Under optimum reaction conditions, the... 

The difference in stability noted above is of the same order of magnitude as that found for the formation of adducts 22 and 23 for the reaction of 1,3,5-trinitrobenzene with the OH" and MeO" ions, respectively. Examination of the activation parameters shows some relevant differences between the heterocyclic and the homocyclic systems, however. The higher reverse rate for the methoxy adduct of trinitrobenzene 23 relative to the corresponding hydroxy adduct 22 is controlled by the higher activation entropy, whereas the higher reverse rate for the methoxy adduct of the dinitropyridine 1 relative to 3 is determined by the activation enthalpy. The entropy effect has been related to the different role of intramolecular interactions of the hydroxy adducts in the benzene and pyridine series. The reason for this difference is still unclear, however.45... 

Tetraalkylammonium fluoride (R4N 1 F ) is well known as being highly receptive to protic compounds such as hydrogen halides and water, affording non-stoichiometric hydrogen-bonded adducts, R N F (HY) , in non-polar solvents. This property reasonably accounts for the hygroscopic nature of ammonium fluorides. However, under strictly anhydrous conditions, intramolecular interactions are predominant and result in self-destruction of the tetraalkylammonium cation via Hoffman elimination to furnish tetraalkylammonium bifluoride, trialkylamine, and olefin (Scheme 9.12) [22]. Consequently, the resulting tetraalkylammonium bifluoride,... 

Furthermore, the geometry of adducts is influenced by the silicon bonded X groups. It should be pointed out that the rotation about the SiY bond is obviously not much hindered therefore, the substituents at silicon are always oriented in such a way in the crystalline phase as to minimize repulsive intramolecular interactions with substituents at Y. Over and above that, it should be noticed that the formation of n-complexes of silenes stabilize the unsaturated systems. 

Dlels-Alder reaction assisted by Intramolecular interactions. The Diels-Alder reaction is one of the most important reactions in organic synthesis and has been applied to the synthesis of various natural products which possess a six-membered ring system. Unfortunately, however, there are some limitations to the structures of dienes and dienophiles that can be used successfully. For example, the Diels-Alder adducts between furan derivative and... 

The reaction mechanism proposed for the LiBr/NEta induced azomethine ylide cycloadditions to a,p-unsaturated carbonyl acceptors is illustrated in Scheme 11.10. The ( , )-ylides, reversibly generated from the imine esters, interact with acceptors under frontier orbital control, and the lithium atom of ylides coordinates with the carbonyl oxygen of the acceptors. Either through a direct cycloaddition (path a) or a sequence of Michael addition-intramolecular cyclization (path b), the cycloadducts are produced with endo- and regioselectivity. Path b is more likely, since in some cases Michael adducts are isolated. 

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