Miscellaneous Ring Closure Reactions

2 Intermolecular S j l Reaction Followed by Intramolecular or BHAS Reaction 

The photostimulated reaction of o-diiodobenzene 131 with 2-naphthoxide ion 65 in liquid ammonia afforded the tetracyclic compound 132 (Eq. 10.45) [92]  

By ET to 131 and after C—I bond fragmentation, the radical 133 is formed, which by couphng with 65 gave finally 134. By ET to 134 and after C—I bond fragmentation, the distonic radical anion 135 was formed, which by a coupling reaction yielded the conjugated radical anion 136, which by ET gave ultimately the product 132 (Eq. 10.46)  

The aryl radical intermediate in reaction can be trapped by an aromatic ring. For example, the reaction of 131 with naphthalene-2-thiolate ions 137 afforded the ring closure product 141 (62% yield) [92]. In this case, by ET to 131 and after C—I bond fragmentation, the 

Finally, the reaction of 1,8-diiodonaphthalene 142 with 4-methylbenzenethiolate ions 143 gave under irradiation the ring closure product 144. The mechanism of its formation is by a consecutive Sj l reaction followed by a HAS reaction (Eq. 10.48) [93], similar to Equation 10.47  

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Miscellaneous Ring-Closure Reactions to Form Two C—N Bonds from a... 

H. MISCELLANEOUS RING-CLOSURE REACTIONS TO FORM DIAZA-CROWN MACROCYCLES... 

Miscellaneous ring closure reactions involving carbon-carbon bond formation are shown in Scheme 72 and 73. An oxidation-cyclization-oxidation process was effected by PCC to convert alcohols 197 to 4-piperidones 198 <04JOC3226>. Intramolecular alkylation was used to covert chiral enaminone 199 to 200, a key intermediate in the total synthesis of lepadin alkaloids... 

Miscellaneous Compounds. A saturated spirocychc pyrrohdine serves as the nucleus for a diamine that has been described as a hypohpemic agent. Treatment of the carbanion of the substituted cylcohexane carboxyhc ester (20-1) with methyl bromoacetate leads to the alkylation and formation of the diester (20-2). Saponification of the ester groups followed by reaction with acetic anhydride leads to ring closure of the succinic anhydride (20-3). Condensation with ammonia leads to the succinimide (20-4). The side chain is then added by alkylation of the anion on nitrogen with l-bromo-4-dimethylaminobutane (20-5). Reaction of this last intermediate with lithium aluminum hydride leads to the reduction of the carbonyl groups to methylene. This affords the pyrrolidine (20-6) atiprimod [22]. 

Heterocyclic ring closure of o-hydroxylated or o-acylated styrene, stilbene, and stilbazole derivatives. This group includes miscellaneous methods, the final stage of which involves ring closure of compounds as in Eq. (2). Starting from o-acyloxystilbenes, the reaction provides... 

The chapter ends with a rather miscellaneous collection of reactions such as one example of an electrocyclic ring closure 19. There are more important examples of ring closing olefin metathesis (RCM) and other organometallic reactions such as the Pauson-Khand reaction and co-trimerisation. 

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