Electrophile-Induced Cyclization

Examples of electrophile-induced cyclization are known to prepare septanosides in recent years. Kover and coworkers reported the first example of preparation of 

SCHEME 13.6 Baeyer-Villiger oxidation to prepare septano-uloside derivatives [18]. 

SCHEME 13.7 Vinyl sulfide synthon to prepare thioseptanoside [19], 

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A. Kover, M. I. Matheu, Y. Diaz, and S. Castillon, A study of the oxepane synthesis by a 7-endo electrophile-induced cyclization reaction of alkenyisulfides. An approach towards the synthesis of septanosides, Arkivoc (2007) 364-379. 

The electrophile-induced cyclization of heteroatom nucleophiles onto an adjacent alkene function is a common strategy in heterocycle synthesis (319,320) and has been extended to electrophile-assisted nitrone generation (Scheme 1.62). The formation of a cyclic cationic species 296 from the reaction of an electrophile (E ), such as a halogen, with an alkene is well known and can be used to N-alkylate an oxime and so generate a nitrone (297). Thus, electrophile-promoted oxime-alkene reactions can occur at room temperature rather than under thermolysis as is common with 1,3-APT reactions. The induction of the addition of oximes to alkenes has been performed in an intramolecular sense with A-bromosuccinimide (NBS) (321-323), A-iodosuccinimide (NIS) (321), h (321,322), and ICl (321) for subsequent cycloaddition reactions of the cyclic nitrones with alkenes and alkynes. 

PhSOMe-BF3 and N-phenylselenylsuccinimide-BFs have also been established as initiators of bicy-clizations (Section 1.9.6.2). Understandably, the electrophile-induced cyclizations are most efficient when the initial reaction occurs at the most nucleophilic double bond. However, these initiators have not been tested with a sufficient range of substrates to allow generalizations about tiieir individual effectiveness. 

An all carbon conjugated ladder polymer (graphite ribbon) was synthesized by a novel electrophile-induced cyclization reaction to provide fused benzenoid aromatic hydrocarbon in quantitative yield [161]. Suzuki cross-coupling of dieneyne 105 with 1,4-didode-cylbenzene-2,5-diboronic acid (106) gave rigid-rod polymers 107, which was further treated with TFA to produce 108 graphite ribbon as a yellow/orange solid. 

Electrophile-induced cyclizations in syntheses of physiologically active azaheterocycles 00JHC607. 

Bravo F, Castilldn S (2001) Synthesis of substituted tetrahydrofuran by electrophile-induced cyclization of 4-pentene-l, 2,3-triols- and example of 5-exo versus 5-endo cyclization governed by the electrophile. Eur J Org Chem 507-516... 

The carbopenam ring system is available by electrophilic induced cyclization of readily obtainable monocyclic azetidinones (Scheme 130). ... 

Fastened parallel 7r-conjugated chains of (CH) can be combined in different ways. Thus, polyphenanthrene can be viewed as the result of various combinations of c -(CH)j chains (Fig. 36). A polymer with a structure close to that of Figure 36 was synthesized by an electrophilic-induced cyclization reaction [277,309] (Fig. 37). A polyphenanthrene derivative with cyclic imine structures has been synthesized by Tour and Lamba [310,676] (Fig. 38). The synthesis is based on Suzuki coupling, followed by a ring closure reaction to form the imine structure. 

Padwa A, Lee HI, Rashatasakhon P, Rose M. Electrophilic-induced cyclization reaction of hexahydroindoli-none derivatives and its application toward the synthesis of ( )-erysotramidine. J. Org. Chem. 2004 69(24) 8209-8218. 

Ohta, Y., and Y. Hirose Electrophile Induced Cyclization of Farnesol. Chemistry Letters 1972, 263. 

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