A New General Synthesis of Benzo[a]quinolizines, Dibenzo[a, f]quinolizines, and Related Compounds

Annelation of 3,4-dihydroisoquinolines by 3-acyl-5,5-dimethylthiopyran-2,4-diones. Synthesis and properties of 8-aza-17-thia-d-homogona-12,17a-diones

“…The proposed mechanism, in contrast to what has been discussed earlier in [9,10,12] and in accordance with the studies in [11], assumes concerted formation of the C-C and C=N bonds, closing the dihydro-γ-pyridinone ring C of product 4 via a six-membered transition state TS. The hypothetical alcohol 6 is either metastable and dehydrated to form the end product under the reaction conditions, or else it is generally not formed as an intermediate but rather the conversion 5 → 3a-d occurs with elimination of a water molecule directly during formation of the pyridone ring C. Considering the data in [26], the second route is preferred.…”

“…In the spectra of derivatives 4b,d, along with what has been indicated, there are also asymmetric absorption bands in the ~230 nm region (of about the same intensity), probably due to electronic transitions of the methoxy-substituted aromatic ring A [5,12,13] and the thiolactone moiety. Evidence in favor of such a conclusion is the fact that the intensity of absorption bands due to only the methoxy-substituted aromatic ring A is generally significantly lower [5,12,13].…”

“…However, the shifts of signals for nuclei far away from the positions where structural changes occur are more meaningful for studying and understanding the stereoelectronic changes in the molecules of the considered series of compounds. Thus the 11-methyl derivatives 4c,d differ from their 11-unsubstituted analogs 4a,b in the signals for the 13 C (9) , 13 C (7) , 13 C (13) atoms that are shifted downfield by ~4.0 ppm, 1.0 ppm, and 1.5 ppm respectively, and also in the signal for the 13 C (12) atom, which is found ~3 ppm upfield. These shifts are certainly connected with differences in the electronic environment of the indicated atoms, and those differences in turn are connected with a change in the planarity of the AAVC moiety.…”

“…A quite promising approach to controlling the immune activity of 8-aza steroids is to introduce additional heteroatoms into their tetracyclic ring [8]. So far 8,16-diaza- [9], 8-aza-16-oxa- [10], 8-aza-16-thia- [11], 8,17-diaza-D-homo- [12], and 8-aza-17-oxa-D-homogonanes have been synthesized and studied [13]. At the same time, compounds in the 8-aza-17-thia-D-homogonane series have been described only recently [14].…”

“…In the electronic absorption spectra of azathia-D-homogonanes 4a,c, there are two intense absorption bands (log ε > 4) at ~270 nm and ~315 nm that are typical of compounds containing an α-acyl-β-aminovinylcarbonyl (AAVC) group N (8) -C (14) =C (13) (-C (12) =O)-C (17/17a) =O [5,11,12]. In the spectra of derivatives 4b,d, along with what has been indicated, there are also asymmetric absorption bands in the ~230 nm region (of about the same intensity), probably due to electronic transitions of the methoxy-substituted aromatic ring A [5,12,13] and the thiolactone moiety.…”