Tandem Dearomative/Rearomative (3 + 2) Annulation of Aroyl-Substituted Donor–Acceptor Cyclopropanes with Benzothiazoles

Abstract

A series of benzo [d]pyrrolo [2,1-b]thiazoles was synthesized by (3 + 2) annulation of aroyl-substituted donor− acceptor cyclopropanes with benzothiazoles. The annulation, promoted by a substoichiometric amount of Sc(OTf) 3 , takes place through the formation of the respective dearomatized (3 + 2) adducts, followed by unexpected decarbethoxylative and dehydrogenative rearomatization to afford fully aromatized products. The unusual reactivity is attributed to the presence of an extra aroyl group in the donor−acceptor cyclopropanes.

Sequential One-Pot Synthesis of β-Amino-γ-keto-malonates from Nitro-Substituted Donor–Acceptor Cyclopropanes

“…Moreover, the reaction did not require the assistance of any reagent or catalyst and is facilitated by the intermolecular hydrogen bonding between the NH group of indoline and the ester carbonyl group of aroylmethylidene malonates. 6,9 It may be noted that indoline is an important structural motif found in many medicinally active natural products and other useful stuffs. 10 Next, we reacted the aroylmethylidene malonates generated in situ from DACs 1 with benzotriazole (6a), 4-methylbenzotriazole (6b), 4-nitrobenzotriazole (6c), benzimidazole (7a), 2-methylbenzimidazole (7b), and 5-chlorobenzimidazole (7c) and obtained a series of benzazolated adducts 10a-i and 11a-i (Table 1, entries 8-16 and 17-25).…”

“…1 H NMR (400 MHz, CDCl 3 ):  = 8.01 (d, J = 8.0 Hz, 2 H), 7.57 (t, J = 7.4 Hz, 1 H), 7.44 (t, J = 7. 6 Hz, 2 H), 7.11 (t, J = 7. 6 Hz, 1 H), 7.01 (d, J = 7.2 Hz, 1 H), 6.77 (d, J = 8.0 Hz, 1 H), 6.65 (t, J = 7.2 Hz, 1 H), 5.93 (d, J = 10.8 Hz, 1 H), 4.52 (d, J = 10.8 Hz, 1 H), 4.26-4.17 (m, 2 H), 3.90-3.80 (m, 2 H), 3.65 (q, J = 9.2 Hz, 1 H), 3.25-3.19 (m, 1 H), 3.02-2.86 (m, 2 H), 1.26 (t, J = 7.2 Hz, 3 H), 1.05 (t, J = 7.0 Hz, 3 H).…”

“…6 Hz, 1 H), 7.01 (d, J = 7.2 Hz, 1 H), 6.90 (d, J = 8.8 Hz, 2 H), 6.77 (d, J = 7. 6 Hz, 1 H), 6.64 (t, J = 7.4 Hz, 1 H), 5.89 (d, J = 10.8 Hz, 1 H), 4.52 (d, J = 10.8 Hz, 1 H), 4.24-4.16 (m, 2 H), 3.86-3.80 (m, 5 H), 3.68-3.61 (m, 1 H), 3.24-3.18 (m, 1 H), 3.01-2.83 (m, 2 H), 1.26 (t, J = 7.2 Hz, 3 H), 1.04 (t, J = 7.2 Hz, 3 H). 13 C{ 1 H} NMR (100 MHz, CDCl 3 ):  = 193.3, 168.…”

“…1 H NMR (400 MHz, CDCl 3 ):  = 7.87 (d,J = 8.4 Hz,2 H),7.58 (d,J = 8.4 Hz, 2 H), 7.12 (t, J = 7. 6 Hz, 1 H), 7.03 (d, J = 7.2 Hz, 1 H), 6.74 (d, J = 8.0 Hz, 1 H), 6.67 (t, J = 7.4 Hz, 1 H), 5.85 (d,J = 10.8 Hz,1 H),4.49 (d,J = 10.8 Hz,1 H),2 H),2 H),1 H), 3.20-3.17 (m, 1 H), 2.98-2.88 (m, 2 H), 1.27 (t, J = 7 Hz, 3 H), 1.05 (t, J = 7 Hz, 3 H). 13 C{ 1 H} NMR (100 MHz, CDCl 3 ):  = 193.8, 167.8, 167.7, 148.4, 138.0, 134.1, 132.1, 130.0, 129.9, 128.91, 128.85, 127.3, 124.9, 118.2, 105.8, 61.86, 61.84, 57.7, 49.5, 46.7, 28.1, 14.0, 13.6.…”

“…6 Hz, 2 H), 7.11 (t, J = 7. 6 Hz, 1 H), 7.01 (d, J = 7.2 Hz, 1 H), 6.77 (d, J = 8.0 Hz, 1 H), 6.65 (t, J = 7.2 Hz, 1 H), 5.93 (d, J = 10.8 Hz, 1 H), 4.52 (d, J = 10.8 Hz, 1 H), 4.26-4.17 (m, 2 H), 3.90-3.80 (m, 2 H), 3.65 (q, J = 9.2 Hz, 1 H), 3.25-3.19 (m, 1 H), 3.02-2.86 (m, 2 H), 1.26 (t, J = 7.2 Hz, 3 H), 1.05 (t, J = 7.0 Hz, 3 H). 13 C{ 1 H} NMR (100 MHz, CDCl 3 ):  = 194.8, 167.96, 167.76, 148.6, 135.4, 133.6, 128.9, 128.7, 128.6, 127.3, 124.8, 117.9, 105.9, 61.80, 61.76, 57.7, 49.6, 46.7, 28.1, 13.9, 13.6.…”