5- exo-trig process

The only reported example of such hydroaminations concerns the IH of a-(aminoalkyl)styrenes (5-Exo-Trig process) (Eq. 4.36) [134]. 

For the alkynyUiydroxylamines 274 smdied by Holmes (309,311), initial intramolecular 1,3-azaprotiocyclotransfer affords the N-oxides 275 via a 5- or a 6-exo-dig process [Baldwin s terminology (312)], which then tautomerize to the cyclic nitrones (276) (Scheme 1.57). The 1-exo-dig cyclization required for the formation of a seven-membered nitrone (277) by this approach from 278 was found to be disfavored with respect to the alternative reaction of hydroxylamine and alkene 5-exo-trig process) to afford a mixture of the alkynylpyiTolidines 279... 

In another experiment (56), the disfavored 5-Endo-Trig process (159) was placed in competition with the favored 5-Exo-Trig process (154). The hydroxy conjugated ester 172 upon treatment with a variety of bases closed efficiently and cleanly to the lactone 173 (5-Exo-Trig process) with no trace... 

A sugar-derived vinyl sulfone (92) was found to undergo a Michael-initiated ring closure (MIRC) process to build up a chiral polysubstituted oxolan system with high stereoselectivity, yielding the all-syn stereoisomer (93) (Scheme 25).61 The observed MIRC selectivity demonstrates that the 5-exo-trig process is strongly... 

Grigg and coworkers have used 2-tributylstannylfuran to terminate a variety of interesting tandem cyclization-anion capture reactions. In one example, aryl iodide 105 reacts via a 5-exo-trig process to provide dihydroindolone 106 [105-107]. 

In further revelation of the strong stereoelectronic requirement for the intramolecular SN2 reaction, the hydroxy ester 156 furnished the lactone 157 only and none of the tetrahydrofuran product 158 on reaction with a base. Whereas the product 157 arises from the 5-exo-trig process involving attack of the oxy anion on the ester carbonyl function, the difficult 5-endo-thg process involving attack of the oxy ion at the olefinic carbon in conjugate fashion is required for the formation of 158 [25, 26]. 

In a competition study, Malacria and co-workers have shown that a 5-exo-dig cyclization is appreciably faster than the 5-exo-trig process [62]. The same group has exploited this... 

The 3-exo-trig cyclization often wins over a 5-exo-trig process, even though both are possible in the second step as exemplified by the cyclization of a triene with two suitable... 

Cathodic reduction of Ai-(2-iodophenyl)-iV-alkylcinnamides under deaerated conditions forms l-alkyl-3-benzylindolin-2-ones regioselectively (70-85%), presumably in a radical or anionic 5-exo-trig process. The mechanism has been explored by the use of cyclic voltammetry, controlled-potential electrolysis (cpe), and deuterium labeling [116],... 

A 5-exo-trig process was reported for the formation of y-lactones by isomerization of a vinyloxirane borne by a steroid skeleton. Yields of these lactones are strongly linked to the preparation of the catalyst. Scheme 14 depicts the key step in the synthesis of Digitoxigenin. 

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