Cyclizations to Aromatic Systems

20/NEt3 or DBU in acetonitrile. Similar condensations of O-silylated y9-dicarbonyl compounds with l,3-bis(trimethylsilyloxy)-l-methoxybutadiene (which is readily obtained by quenching of the anion of methyl 3-trimethylsilyloxybut-2-enoate with Me3SiCl 14, at -78 °C in CH2CI2, in the presence of Lewis acids such as TiCL ) likewise afford O-silylated methyl salicylates in high yields [40a-d]. 

Heating of hexane-2,5-dione 1487 with TCS 14, Nal, and triethylamine for 36 h, to form 1488, followed by addition of triflic acid and heating to 140 °C affords, on distillation, a mixture of 2,5-dimethylfuran 1489 and HMDSO 7 containing 90% 

As already discussed in Section 5.5.2, amidine hydrochlorides 743 react with O-silylated methyl (or ethyl) 4-chloroacetoacetate 746, in which the 4-chlorine atom 

Phenyl N-acetylcarbazate 1529 cyclizes on boiling with excess TCS 14/tri-ethylamine in toluene to give 5-methyl-l,3,4-oxadiazohne-2-one 1530 in 65-70% yield [41, 59, 60]. The same type of cyclization was subsequently described for re- 

Heating of N-acetylsemicarbazide 1536 with HMDS 2 and triflic acid in chlorobenzene to 100°C affords 5-methyl-l,2,4-triazole-2-one 1537 [41]. Likewise, the 

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Menes-Arzate M, Martinez R, Cruz-Almanza R, Muchowski Joseph M, Osomio Yazmin M, Miranda Luis D (2004) Efficient, tin-free radical cyclization to aromatic systems. Synthesis of 5,6,8,9,10,ll-hexahydroindolo[2,l-a]isoquinolines. J Org Chem 69 4001-4004... 

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