Intramolecular electrophilic reaction group

Intramolecular electrophilic reaction of (y3-silylmethyl)allylsilane with an imino group is an efficient approach to an l-azabicyclo[3.2.1]octane framework [32]. For example, treatment of 94 with formaldehyde in CH3CN at room temperature and then with trifluoroacetic acid produces 97 as a trifluoroacetate salt, presumably through domino cydization through 95 and then of 96 (Scheme 5.24). 

The Yao group has made use of a Ic type intramolecular Heck reaction to prepare the C2-symmetric dimeric indole core of chloptosin <06OL4919>. A solvent-free variation of the Bischler indole synthesis, electrophilic cyclization of a-arylamino imine tautomers prepared from aniline derived a-arylamino ketones, has been used by Menendez and co-workers for the preparation of 2-arylindoles <06SL91>. 

The reaction of 2-chloro-4,5-dihydroimidazole 347 with hydroxylamine-O-sulfonic acid gives 2-hydroxylamino-4,5-dihydroimidazolium-O-sulfonate 348, which reacts with aldehydes and cyclic ketones to give the imidazo[l,2-f] fused 4,5-dihydro-l,2,4-oxadiazoles 350 (Scheme 58). Mechanistically, the reaction may be explained by the reaction of an imidazoline NH with the carbonyl followed by intramolecular electrophilic amination of the anionic oxygen present in the resultant intermediate 349 and elimination of the sulfate group <2003JOC4791>. 

Radical anions resulting from cathodic reductions of molecules react with electrophilic centers. As an example (Scheme 8), the reduction of compounds in which a double bond is not conjugated with a carbonyl group, involves an intramolecular coupling reaction of radical anion with alkene [12]. 

Fig. 14. Manifold of reactive species produced from the reaction of a heme group with oxygen and two reducing equivalents. The rate of conversion of A to B limits the lifetime (and therefore reactivity) of the Fe peroxo anion. The rate of formation of the ferryl species C via the Fe -OOH complex B competes with the intramolecular hydroxylation reaction to give hydroxyheme. Reactions of the Fe -hydroperoxy complex B with exogenous electrophilic substrates must compete with conversion of the intermediate to both C and meso-hydroxyheme. The Fe -OOH complex B can also be formed directly with H2O,.

The results are explained as indicating that the addition of triplet arylcarbenes to intramolecular double bonds is accelerated by factor of 300-800 relative to inter-molecular addition. The intramolecular addition reactions of singlet arylcarbenes exhibit much smaller rate enhancements. The most stable planar conformer of singlet (102) cannot interact with the n bond of an allyl group attached to the ortho position. Rotation about the bond connecting the divalent carbon to the ring must occur in order for an electrophilic approach to take place. This rotation will result in the loss of benzylic stabilization. In marked contrast, the first step of the triplet addition can take place with no rotation of the divalent carbon. 

Transesterification reactions of 2-alkoxycarbonylethyltin trichlorides and their adducts with neutral donors with alcohols proceed readily. This is attributed to the intramolecular Lewis catalysis by the electrophilic SnCl group owing to the coordination of the ester carbonyl group to the tin atom, C = O —Sn, which decreases the electronic density at the carbonyl carbon atom727,741 745 754. 

They can also be obtained from alkenes in a two-step process (Fig. A). The first step involves electrophilic addition of a halogen in aqueous solution to form a halohydrin. Treatment of the halohydrin with base then ionises the alcohol group, that can then act as a nucleophile. The oxygen uses a lone pair of electrons to form a bond to the neighbouring electrophilic carbon, thus displacing the halogen by an intramolecular SN2 reaction. 

Whereas a triplet 1,4-biradical has been assigned as the most probable intermediate at that time, later work on intramolecular trapping reaction favored the assumption of radical ion pairs [46]. Efficient lactonization reaction to form 51 during irradiation of pent-4-enoic acid 50 and 48 accounts for an olefin radical cation which undergoes electrophilic addition towards the carboxyl group. Another type of rearrangement has been detected in the photoreaction of tetramethylallene and 48 [47]. 5-Hydroxy-indan-2-ones 52 are formed in high yields probably via instable spiro-oxetanes 49b as intermediates. 

Another type of intramolecular electrophilic substitution is shown in Equation (1).25 In this case, the reaction sites are located in different substituents on silicon. This reaction mode is useful for highly diastereoselective alkenylation and phenylation of aminoacetals and hemiaminals.26 Intramolecular conjugative arylation of a-enals bearing an aryldimethylsilyl group is effectively promoted by tetrabutylammonium fluoride (TBAF) (Equation (2)).27,27a... 

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