Trapping, intramolecular nucleophilic

The advantage of the nitro group as radical precursor is best seen in the context of intramolecular nucleophilic trapping of alkene radical cations by nitrogen nucleophiles, when no cyclization was observed prior to treatment... 

There are a number of important reactions in this category and all of them involve at least one heteroatom functioning as a nucleophile and another as an electrophile. Diazo-tization of a variety of ortho-substituted anilines for instance, followed by intramolecular nucleophilic trapping of the corresponding diazonium salts by either nitrogen or carbon nucleophiles, is the basis of a series of very important syntheses of 1,2,3-benzotriazine and cinnoline derivatives, and this general approach has been widely exploited for the preparation of polycyclic systems. Representative examples are given in equations (51)—(54). 

Both reaction modes A and B have been observed for carbopalladations of methylenecyclopropane derivatives 59a,b with subsequent intramolecular nucleophilic trapping of the intermediate allylpallatium species in or IV, respectively, depending on the tether lengths between the methylenecyclopropane and the dimethyl malonate moieties. The same carbopalladations of unsubstituted methylenecyclopropane 43 (=60a) and pentyli-dene-cyclopropane (60b) with subsequent intermolecular trapping by carbon nucleophiles were found to generally proceed by mode B via intermediates II, V, IV to yield ringopening products 61 and 62, respectively (Scheme 16). 

D. INTERMOLECULAR CARBOPALLADATION OF ALLENES FOLLOWED BY INTRAMOLECULAR NUCLEOPHILIC TRAPPING... 

The as-fused fiirobenzopyranone of 12-hydroxymonocerin was efficiently constructed via an intramolecular nucleophilic trapping of a qui-nonemethide intermediate, which was obtained by benzylic oxidation using 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) (13T11025). 

Gold-catalysed ene-yne cyclization has been employed in two closely related and simultaneous syntheses of englerin A 6.278, a sesquiterpene that has shown anti-tumour activity (Scheme 6.111). Both syntheses relied upon the intramolecular nucleophilic trapping of the cyclopropyl carbene intermediate 6.280 by a ketone nucleophile, followed by counterattack of the anionic t -vinyl gold species onto the oxonium ion 6.281 formed in this way, to form the skeleton of the molecule, but differed in their approach to the other functionality. 

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