An Intramolecular Ring Closure

Treatment of the amide 1 with TFAA in methylene chloride at 25°C gave 2 in 85% yield. Suggest a mechanism for this transformation. 

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The addition of nucleophiles to double and triple bond systems is often a convenient way of effecting an intramolecular ring closure. Addition to cyano groups has received considerable attention, as in addition to ring formation it provides a convenient method for the introduction of an amino group. Reaction of methyl Af-cyanodithiocarbimidate with Af-methylaminoacetonitrile resulted in displacement of methanethiol and formation of (314). Sodium ethoxide treatment in DMF converted (314) into a 4-amino-5-cyanoimidazole... 

The antiaromatic twelve r-electron benzodithiadiazine 12.12 (R = H), an inorganic naphthalene analogue, is obtained as a volatile deep-blue solid by the reaction of PhNSNSiMcs with SCI2, followed by an intramolecular ring closure with elimination of HCl (Scheme 12.2). ... 

The antiaromatic 12 re-electron benzodithiadiazine 95 (R=H) is obtained as a volatile deep blue solid by the reaction of PhNSNSiMe3 with SC12, followed by an intramolecular ring closure with elimination of HC1.247 The tetrafluoro derivative 95 (R=F) is prepared by treatment of C6F5SNSNSiMe3 with CsF in acetonitrile.248 Several difluoro- and trifluoro-benzodithiadiazines have also been prepared by these methods.249 In contrast to essentially planar 95 (R=H),247 the dithiadiazine ring in the tetrafluoro derivative is somewhat twisted.248 In the gas phase, on the other hand, 95 (R=F) is planar, whereas 95 (R=H) is non-planar.25,249... 

The reduction of Cl3SiC6H2-2,4,6-Ph3 with lithium metal in the presence of trimethylsilyl chloride led to the isolation of a silafluorene compound that was formed by an intramolecular ring closure.100 Although the mechanism is unknown, it is believed that reduction affords a silyl radical, which may... 

The product is omega-caprolactone, a seven membered lactone that cannot be made by an intramolecular ring closure. 

Apparently, the first N-arylation had proceeded well, but then an intramolecular ring closure occurred faster than the second coupling reaction, thereby convert-... 

A similar approach was used by Mihailovic and coworkers.16 When 2-te-trahydrofuranethanol (119) was treated with lead tetraacetate, an intramolecular ring-closure occurred, to give a 45% yield of (R, flJ-m-2,6-dioxabicy-clo[3.3.0]octane (115), together with seven other compounds in minor proportions. Compound 115 was prepared from D-mannitol by following the established procedure of Cope and Shen,193 and was used as an intermediate for the first synthesis of thiacyclodeca-4,7-diene.200 Finally, several... 

An intramolecular ring closure is reported to give the pyrimido[4,5-c][l,2]oxazines (193) and (195) (Scheme 33). Starting from a 5-(2-chloroethyl)-l-methyluracil (191) which is converted into the... 

Scheme 9.4 Problems encountered during opening of typical epoxide intermediate (see also Section 9.4, Chemical Synthesis) when intended N-external ester substituents do not bear alpha-substituents [10]. A Normal, well-behaved reaction as typically deployed for beta-blockers wherein the N-alkyl group bears an alpha-substituent as most commonly represented by isopropylamine. B The over-alky-lation problem that occurs significantly when the N-alkyl group is not alpha-substituted. Also note that when n = 3 or 4, the first alkylation is instead followed immediately by an intramolecular ring-closure reaction to form the five- or six-membered lactam. These unwanted side products, although readily...

As a side product, a new six-membered ring system was obtained. Three aldol condensation reactions of phenylmethylketone occurred. The last one led to an intramolecular ring closure. 

As with pentafulvalene, an extended h eptafulvalene (XXXIT") has been prepared [253]. This is a red-brown crystalline compound which decomposes in air within one day, although it is moderately stable in solution in carbon tetrachloride. Above 60 it undergoes an intramolecular ring-closure [254]. 

Your team is studying the problem of an intramolecular ring closure of enediyne systems important in the total synthesis of dynemicin A, which exhibits potent antitumor activity. 

The development of catalytic, enantioselective C-H insertion reactions has been relatively slow in comparison with the diastereoselective variants described in Section 15.7. It was only in 1990 that McKervey reported the first such example in the context of an intramolecular ring closure (Equation 28) [51]. Exposure of 169 to chiral rhodium catalyst 170 thus afforded 171 in 12% ee. 

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