Erythrina and Related Alkaloids

C-10b Functionalized 5,6-dihydropyrrolo[2,1-a]isoquinolines as intermediates in the synthesis of erythrinane systems. Intra- vs. intermolecular conjugate addition based strategies

“…In this context, we had previously reported that 2-(3-lithiopropyl)-2-trimethylsilyl-1,3-dithiane 6c (Figure 1) may be used in this addition-α-amidoalkylation sequence for the synthesis of functionalized dihydropyrroloisoquinolines of general structure 2a. 3d However, desilylation was problematic, decided to test other possible 1,4-dianion equivalents, and selected protected β-carbonylorganolithiums, as 2-(2-lithioethyl)-2-methyl- [1,3]dioxolane 6a and 2-(2-lithioethyl)-2-methyl- [1,3] dithiane 6b ( Figure 1). …”

“…In all cases, no reaction was observed with 2a, recovering starting material, while 2b led to a mixture of products. To check that the enolate was being efficiently formed, we carried out the deprotonation with LDA at -78 °C, and quenched the reaction with TMSCl, obtaining the corresponding enol ethers that could be characterized by 1 In view of these results, we thought of an alternate route that would involve an intermolecular conjugate addition. Thus, ring A of the erythrinane system could be assembled through the ring-closing metathesis (RCM) reaction of pyrroloisoquinolones 10.…”

“…This activity is attributed to antagonistic action of the nicotinic acetylcholine receptors in the brain. 1 Because of their unique spiro amine structure and physiological activities, these alkaloids have been a target of synthesis for a long time. 2 Over the last years we have developed 3 new procedures for the synthesis of tetrahydro-and dihydropyrroloisoquinolones based on organolithium 4 and N-acyliminium chemistry.…”

Acid-Promoted Cyclization Reactions of Tetrahydroindolinones. Model Studies for Possible Application in a Synthesis of Selaginoidine

“…The solution was extracted with ether and the combined ether extracts were washed with brine, dried over MgSO 4 , filtered and concentrated under reduced pressure. The crude product was subjected to flash silica gel chromatography to give 1.9 g (73%) of methyl 4-bromo-5-(3-oxopropyl)furan-2-carboxylate as a colorless oil: 1 H-NMR (CDCl 3 , 400 MHz) δ 2.90 (t, 2H, J = 6.8 Hz), 3.04 (t, 2H, J = 7.6 Hz), 3.87 (s, 3H), 7.11 (s, 1H), and 9.83 (s, 1H); 13 …”

“…The organic layer was dried over MgSO 4 , filtered and concentrated under reduced pressure. The crude azide was subjected to flash silica gel chromatography to give 0.47 g (93%) of azide 53 as a yellow oil; IR (thin film) 2951, 2108, 1739, and 1315 cm −1;1 H-NMR (CDCl 3 , 400 MHz) δ 1.96 (p, 2H, J = 7.2 Hz), 2.82 (t, 2H, J = 7.2 Hz), 3.33 (t, 2H, J = 6.8 Hz), 3.87 (s, 3H), and 7.12 (s, 1H); 13 -5-[3-(3a-methyl-2-oxo-2,3,3a,4,5,6-hexahydroindol-1-yl)propyl]-furan-2-carboxylic Acid Methyl Ester (56)…”