Intermolecular trapping

Bischler-Napieralski reactions of N-acyl tryptamine derivatives 16 are believed to proceed via a related mechanism involving the initial formation of intermediate spiroindolenines (17) that rearrange to the observed 2-carboline products (18). The presence of these intermediates has been inferred by the observation of dimerized products that are presumably formed by the intermolecular trapping of the spiroindolenine by unreacted indole present in the reaction mixture." ... 

As early as 1986, Stork and coworkers presented an intramolecular radical cycli-zation/intermolecular trapping methodology within their synthesis of prostaglandin F2a [58],... 

The first example of an intermolecular radical addihon/intermolecular trapping domino reactions of an acyclic system in a stereocontrolled fashion to build stereo-genic centers at the a- and 3-carbons was described by Sibi and coworkers [59]. Enantioselective addition of in-sitw-prepared alkyl radical to crotonate or cinnamate,... 

Table 5.1. Synthesis of tetralines by intermolecular trapping of hydroxy-o-quinodimethanes.

Only a few examples exist for the intermolecular trapping of allyl radicals with alkenes68,69. The reaction of a-carbonyl allyl radical 28 with silyl enol ether 29 occurs exclusively at the less substituted allylic terminus to form, after oxidation with ceric ammonium nitrate (CAN) and desilylation of the adduct radical, product 30 (equation 14). Formation of terminal addition products with /ram-con figuration has been observed for reaction of 28 with other enol ethers as well. 

With addition hexamethylphosphoramide (HMPA). cWith addition RCOCH=CH2 for intermolecular trapping of SENA. After elimination of Me3 Si OH from [3 +2]-cycloaddition s product. 

Scheme 4.34 Intermolecular trapping of an amide derived ylide.

Intermolecular trapping of carbene complexes (39) has also been reported. In this case, a second carbene (41) arising from a cyclopropyl shift from (39) can also be trapped to yield (42).39... 

De Meijere and co-workers have extended the scope of this process by applying this palladium-mediated multicomponent reaction to the bicyclopropylidene 72 as the alkene partner (Scheme 8.33). In this case, the intermolecular trapping of 7r-allyl palladium intermediate 73 with a soft carbonucleophile or with primary or secondary amines affords only products 74 having a methylenecyclopropane end group [78],... 

Scheme 4.19. Intermolecular trapping of the allyl cation by indole nucleophiles.

Intermolecular trapping of PET generated iminium cations by Me3SiCN have been recently reported by Santamaria et al. [95] for synthesizing a-amino nitriles (e.g. 95-96) in the alkaloid field and also for preparing 6-cyano 1,2,3,6-tetrahydropyridine (98) [96] from 1,2,3,6-tetrahydropyridine (97). Similar cyan-ation of catharanthine alkaloids has also been reported by Sundberg recently... 

This thermal rearrangement, which is the formal result of a orbital symmetry forbidden. Rather, an homolytic cleavage of the cyclopropane bond, giving rise to a trimethylenemethane, would be involved. This rearrangement was the first reported intramolecular trapping of a trimethylenemethane by a double bond (for a related intermolecular trapping of trimethylenemethane by butadiene see Ref 49). On further heating to 600°C, the main product obtained was isopropylcyclo-octatetraene (29) (equation 22f. ... 

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