Annulation reactions annelation

The efficient synthesis of dithicno[2,3-A 32 -r/ thiophenes 12 has been achieved from 3-bromothiophene 298 <2006JOC3264>. The sequence of a-connection and [l-annelation afford annulated [1-trithiophene 12 (Scheme 54). Optimization of reaction conditions (solvent and temperature) for the a-connection step provides significantly improved yields compared to earlier report. 

Annelation-ring cleavage.1 A bifunctional reagent with an acetal and an allylsi-lane group can be used for annulation of silyl enol ethers to six- and seven-membered carbocycles (equation I).2 The reaction involves conjugate addition to give an adduct that undergoes intramolecular cyclization. 

Rele, D., Trivedi, G. K. Recent developments in Michael reaction a convenient tool for annelation and annulation. J. Sci. Ind. Res. 1993,... 

Multicyclic ring systems are also found to be present in synthetic heterocyclic pharmaceuticals. These drugs may be benzo derivatives of monocyclic heterocycles or they may contain other fused-on (said to be annelated or annulated) heterocyclic rings. An important example of a dibenzo derivative, namely, a derivative of the tricyclic phe-nothiazine ring system, is the valuable antihistamine methopromazine (9.142). Its synthesis employs conventional reactions of aromatic chemistry to constmct the interior thiazine ring, as is outlined in Scheme 9.84. 

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