Thieno azocines, synthesis

In recent years much attention has been paid to the synthesis of benzomorphane heteroanalogs in which a benzene ring has been replaced by a heteroaromatic one. Syntheses of substituted thieno[3,2-/]morphanes (derivatives of thieno[2,3-d]-azocine) described in Ref. 75JHC651 consists of the condensation of cyanopyri-dines 120 with 2-thienyllithium, reduction of the resulting ketones into thienylmethylpyridines, quaternization and reduction of the quaternary salts with sodium borohydride to form piperidines 124 and 125. Intramolecular cyclization of the latter leads to the formation of thieno[2,3-d]azocines 126 (Scheme 34). 

For the synthesis of isomeric thieno[3,2-d]azocines 138, intramolecular cyclization of 2-thienyltetrahydropyridines 137 has been used (74JHC853 Scheme 37). 

This reaction was later used successfully for the synthesis of annulated azocines including tetrahydroazocino[4,5-l7] 231 - and azocino[5,4- 7]indoles 232 (04EJO(14)3128), tetrahydropyrimido[4,5-d]azocines 233 (06TL999), tetrahydro-benzo[ 7]thieno[3,2-d]azocines 234 (05CH944) and tetrahydrobenzo[d]azocines 235 (06TL4585 Scheme 64). 

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