Transannular ring closure

Schiff bases have been used in electroreductive cyclizations, leading to heterocyclic compounds. The bisimine (24), when reduced in glyme, affords the piperazine (25) in 42% yield after quenching with methyl iodide (equation 10). When the solvent is changed to dimethylformamide, saturation of the imino bonds takes place without ring closure. Transannular ring closure of diazocine (26) led to indolo-... 

Transannular interactions lead to ring closures and reductions to adamantane compounds when dienes of the bicyclo[3.3.1]nonane family are treated with Brpnsted acids and triethylsilane. Compounds 48-51 form reaction mixtures containing various amounts of products 52-54 (R = OH, O2CCF3, Cl) under such conditions.243 The best yields of hydrocarbon 52 occur when the dienes are treated with a 25% excess of sulfuric acid and a 50% excess of triethylsilane in dichloromethane at 20°.243 The stereospecific nature of these transannular reductions is demonstrated by the observation that the enantiomeric purity of the chiral diene 55 is retained in the chiral hydrocarbon product 56 (Eq. 98).243 Dienes of... 

Similar low activities were found in the hydrogenation of 1-octene [47]. The use of [Ni(PPh3)2I2] in the hydrogenation of norbomadiene resulted in considerable amounts of nortricyclene, via transannular ring closure, whereas 1,5-cyclo-octadiene yielded bis-cyclo-[3.3.0]oct-2-ene. According to these authors, the re-... 

Just one reaction has been described where lithiated methoxyallene 42 reacted with bicyclo[3.2.0]heptenone 175 to form the triquinane derivative 176 via a tandem oxy-Cope-transannular ring closure sequence (Eq. 8.31) [111]. However, cycloocta-none 177 was isolated as a major product, which is unusual since other alkenyl-lithium compounds and 175 provide only triquinanes. The authors assumed that the additional sp2-hybridized C-atom in the eight-membered ring intermediate (eno-late of 177) induces a conformation which is less susceptible to transannular ring closure. 

The unique molecular geometry of the [2.2]paracyclophane system is demonstrated by the ability of the [4.4]paracyclophane 80a [n = 4) to undergo transannular ring closure 80-+81 37>, whereas no ring closure occurs when n =2 21K... 

The mechanism of the dehydrogenative transannular ring closure of cycloocta-tetraene in the presence of various inorganic reagents to provide complexes of pentalene has been the subject of debate... 

No photochemical rearrangements or transannular ring closure chemistry were observed with the corresponding cyclopentadienyl analogues (see Section VIII,A), illustrating the key role of the pentamethylcyclopentadienyl... 

In addition to the facile aluminum halide and sulfuric acid catalyzed rearrangement routes to noradamantane and substituted noradamantanes discussed above (see Eq. (11) and Scheme 8), a variety of ring closure reactions have also been employed for the preparation of these systems. The most useful reaction for this purpose involves a transannular ring closure of the bicyclo [3.3.1 Jnonyl system. Thus, 7-methyl-3-noradamantanol is obtained 12°) from the treatment of 3-keto-7-methylenebicyclo[3.3.1 jnonane 121) with sodium in moist ether (Eq. (36)). 

Photochemically induced transannular ring closure of bicyclo[3-3.1 -nonane-3,7-dione to 3,7-noradamantane diol is illustrated in Eq. (38)12S). 

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