Cyclisation of Benzo[B]Thiophen-3(2H)-One 1,1-Dioxide and 1,3-Indanedione into Novel Methylene Bridged Polycyclic Diazocines and Their Rearrangement into Spirocyclic Compounds

Methylene bridged polycyclic diazocines 2a and 2b were obtained in reactions of 1,3-indanedione, or benzo[b]thiophen-3(2H)one-1,1-dioxide, or 2,2′-methylene derivatives 3a,b with paraformaldehyde and ammonia or hexamethylenetetramine in acidic medium. A structural revision of methylene bridged benzothieno-diazocine 2b based on results of X-ray diffraction analysis is presented. Internal rearrangement of methylene bridged polycyclic diazocines into spiroheterocycles 4a,b is also describe

Contrasting Behaviour of NBS towards 1,4-Dihydro-Benzothieno[3,2-B]Pyridine 5,5-Dioxides and 4,5-Dihydro-1H-Indeno[1,2-B]Pyridines

Polycyclic 1,4-dihydrobenzothieno[3,2-b]pyridine 5,5-dioxides and 4,5-dihydro-1H-indeno[1,2-b]pyridines having ester or cyano group at the position 3 of dihydropyridine ring have been synthesised. Reactivity of N-bromosuccinimide (NBS) towards polycyclic 1,4-dihydropyridine derivatives has been investigated. It has been found that 1,4-dihydrobenzothieno[3,2-b]pyridine 5,5-dioxides are easily oxidised with NBS in methanol at rt in high yields, whereas 4,5-dihydro-1H-indeno[1,2-b]pyridines in reaction with NBS in methanol are brominated at 4a position affording stable 4a-bromo-4a,5-dihydroindeno[1,2-b]pyridine-3-carboxylates or unstable 3-carbonitriles, which rapidly undergo dehydrobromination reaction leading to the corresponding 5H-indeno[1,2-b]pyridine-3-carbonitriles