Combination intramolecular

If an open-chain organic molecule contains an electron acceptor and an electron donor site, two carbon atoms may be combined intramolecularly. This corresponds to the synthesis of a monocyclic compound. 

These fragments either combine intramolecularly to form the ortho and para nitro compounds or dissociate completely and then undergo an intermolecular reaction to form the same products. The theory was not developed to include a detailed transition state and no mention was made of how the para isomer was formed. Reduction of the cation-radical could give the amine (which was observed experimentally76), but one would expect the concurrent formation of nitrogen dioxide and hence nitrite and nitrate ions however, the latter has never been... 

Appropriate combinations of boronic acid and fluorophores lead to a remarkable class of fluorescent sensors of saccharides (Shinkai et ah, 1997, 2000, 2001). The concept of PET (photoinduced electron transfer) sensors (see Section 10.2.2.5 and Figure 10.7) has been introduced successfully as follows a boronic acid moiety is combined intramolecularly with an aminomethylfluorophore consequently, PET from the amine to the fluorophore causes fluorescence quenching of the latter. In the presence of a bound saccharide, the interaction between boronic acid and amine is intensified, which inhibits the PET process (Figure 10.42). S-l is an outstanding example of a selective sensor for glucose based on this concept (see Box 10.4). 

Other 1,2-isomerases combine intramolecular transfer and solvent exchange to various extents,1" 141 but, with D-xylose ketol isomerase, solvent exchange was not found,140 although there is no evidence that the mechanism operates by other than an enediol intermediate. Lack of solvent exchange alone, therefore, cannot be used to exclude the possibility of an enediol intermediate in an enzyme reaction. 

Simple double aza-Michael reaction of divinyl ketones with primary amines was utilized to generate TV-substituted 3-phenyl-4-piperidones in good yields <07EJO4376>. In a somewhat similar mode, the diastereoselective synthesis of cyclic (3-amino esters by an Sn2 substitution-cyclization of an iodo-a,(3-unsaturated ester with (.Sj-u-mcthy 1 benzylamine was described <07OBC3614>. A combination intramolecular Michael-type addition followed by retro-Michael elimination was exploited in the generation of a phosphoryl dihydropyridone intermediate in the synthesis of /m .v-2,6-disubstitutcd 1,2,5,6-tetrahydropyridines <07JOC2046>. 

S. Valverde, M. Garcia, A. M. Gomez, and J. C. Lopez, A combined intramolecular-intermolecular one-pot glycosylation approach for the synthesis of a branched trisaccharide, Chem. Commun., (2000) 813-814. 

A new diastereoselective route to aromatic cw-erythrinanes represents the combined intramolecular Strecker and Bruylants reactions of the phenethyl-cyclohexanylethylamines 88 (Scheme 11). Deprotection of the carbonyl function and addition of potassium cyanide causes the Strecker reaction to give the angularly substituted hydroindole derivatives 89 in nearly quantitative yields. Then the Bruylants reaction is... 

Reimann E, Ettmayr C (2004) An Improved Stereocontrolled Route to m-Erythri-nanes by Combined Intramolecular Streckerand Bruylants Reaction. Monatsh Chem 135 1143... 

Aube and Golden (dJ) have demonstrated the utility of a combined intramolecular Diels-Alder/intramolecular Schmidt reaction to construct the azepinoindole intermediate 110 (Scheme 5). The Lewis add-catalyzed tandem intramolecular Diels-Alder/Schmidt reaction required azidodiene 109, which was prepared after five steps as a 85 15 mixture of diastereoisomers from diene 108 via a modified Julia olefination between aldehyde... 

A number of issues need to be addressed before this method will become a routine tool applicable to problems as the conformational equilibrium of protein kinase. E.g. the accuracy of the force field, especially the combination of Poisson-Boltzmann forces and molecular mechanics force field, remains to be assessed. The energy surface for the opening of the two kinase domains in Pig. 2 indicates that intramolecular noncovalent energies are overestimated compared to the interaction with solvent. 

In the synthesis of molecules without functional groups the application of the usual polar synthetic reactions may be cumbersome, since the final elimination of hetero atoms can be difficult. Two solutions for this problem have been given in the previous sections, namely alkylation with nucleophilic carbanions and alkenylation with ylides. Another direct approach is to combine radical synthons in a non-polar reaction. Carbon radicals are. however, inherently short-lived and tend to undergo complex secondary reactions. Escheirmoser s principle (p. 34f) again provides a way out. If one connects both carbon atoms via a metal atom which (i) forms and stabilizes the carbon radicals and (ii) can be easily eliminated, the intermolecular reaction is made intramolecular, and good yields may be obtained. 

A combination of conju gate addition of an enolate anion to an a p unsaturated ketone with subsequent intramolecular aldol condensation... 

Robinson annotation (Section 18 13) The combination of a Michael addition and an intramolecular aldol condensation used as a synthetic method for nng formation... 

Influence of the Fiber. In order for a dye to move from the aqueous dyebath to the fiber phase the combination of dye and fiber must be at a lower energy level than dye and water. This in turn implies that there is a more efficient, lower energy sharing of electrons or intramolecular energy forces, and there are a number of mechanisms that allow this to happen. 

The thirty-two silent modes of Coo have been studied by various techniques [7], the most fruitful being higher-order Raman and infra-red spectroscopy. Because of the molecular nature of solid Cqq, the higher-order spectra are relatively sharp. Thus overtone and combination modes can be resolved, and with the help of a force constant model for the vibrational modes, various observed molecular frequencies can be identified with specific vibrational modes. Using this strategy, the 32 silent intramolecular modes of Ceo have been determined [101, 102]. 

Either UV-VIS or IR spectroscopy can be combined with the technique of matrix isolation to detect and identify highly unstable intermediates. In this method, the intomediate is trapped in a solid inert matrix, usually one of the inert gases, at very low temperatures. Because each molecule is surrounded by inert gas atoms, there is no possiblity for intermolecular reactions and the rates of intramolecular reactions are slowed by the low temperature. Matrix isolation is a very useful method for characterizing intermediates in photochemical reactions. The method can also be used for gas-phase reactions which can be conducted in such a way that the intermediates can be rapidly condensed into the matrix. 

As is clear from the preceding examples, there are a variety of overall reactions that can be initiated by photolysis of ketones. The course of photochemical reactions of ketones is veiy dependent on the structure of the reactant. Despite the variety of overall processes that can be observed, the number of individual steps involved is limited. For ketones, the most important are inter- and intramolecular hydrogen abstraction, cleavage a to the carbonyl group, and substituent migration to the -carbon atom of a,/S-unsaturated ketones. Reexamination of the mechanisms illustrated in this section will reveal that most of the reactions of carbonyl compounds that have been described involve combinations of these fundamental processes. The final products usually result from rebonding of reactive intermediates generated by these steps. 

The Reforrnatsku reaction of a-halogenated carboxylic esters with silylated cyanohydrins combined with an intramolecular acylation reaction gives fluorinated derivatives of tetronic acid [28] (equation 17) It is noteworthy to mention that this particular reaction sequence only proceeds with ultrasonic irradiation A very... 

Conversion to dialkyl ethers (Section 15.7) On being heated in the presence of an acid catalyst, two molecules of a primary alcohol combine to form an ether and water. Diols can undergo an intramolecular condensation if a five-membered or six-membered cyclic ether results. 

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