Cycloaddition of Azosulfones and Sulfonylimines

Accessing the Rare Diazacyclobutene Motif

“…3,4 Thus, these molecules, their potential aromaticity, and their putative reactivity have been the subject of several computational 5−9 and comparatively fewer synthetic studies. 5,10−13 Despite the first report on the preparation of a small set of stable diazacyclobutenes appearing over half a century ago, 10 less than 10 examples of this scaffold are known (1−4), and typically have been accessed in rather poor yields. 5,10−13 With an interest in accessing this interesting and relatively unexplored scaffold, we set out to develop a convenient method to synthesize diazacyclobutenes.…”

“…The diazacyclobutenes ( 1 – 4 , 6 ) are a unique class of four membered heterocycles consisting of a carbon–carbon double bond and two adjacent nitrogen atoms (Scheme ). Historically, these heterocycles gained attention in the literature owing to the electronic framework resident in the moiety that formally follows the Hückel (4 n +2) rule of aromaticity. , Thus, these molecules, their potential aromaticity, and their putative reactivity have been the subject of several computational − and comparatively fewer synthetic studies. ,− Despite the first report on the preparation of a small set of stable diazacyclobutenes appearing over half a century ago, less than 10 examples of this scaffold are known ( 1 – 4 ), and typically have been accessed in rather poor yields. ,− …”

Addition of dimethyl acetylenedicarboxylate to imino ethers. Trapping of a 1,4-dipolar intermediate

“…Reaction of DMAD with 20a in the Presence of Water. Following the preceding procedure for preparation of 24, 5.31 mg (4.70 mmol) of 20a, 673 mg (4.73 mmol) of DMAD, and 110 mg (6.10 mmol) of water gave 464 mg (38%) of product 25a: bp 120-140°( 0.1 mm); ir (CCL,) 3300, 2950, 1745, 1670, 1620, 1445 cm'1; NMR (CCL,) 1.83 (m, 2 H), 2.32 (m, 2 ), 3.40 (m, 2 H), 3.68 (s, 6 H), 3.85 (s, 3 ), 5.00 (s, 1 H), 8.15 (br d, 1 H); mass spectrum (Finnigan) (50 eV) 260 (0.07), 259 (M\ 0.2), 228 (0.6), 227 (0.6), 212 (0.3), 200 (0.5), 196 (4), 195 (5), 180 (1), 172 (6), 168 (2), 167 (2), 166 (1), 154 (9), 153 (3), 141 (6), 140 (31), 136 (2), 128 (4), 126 (7), 125 (3), 112 (26], 108 (23), 101 (43), 100 (7), 94 (5), 82 (16), 69 (23), 68 (23), 59 (100), 55 (18), 54 (10), 53 (13), 45 (28), 43 (10), 42 (15), 41 (43), 39 (10). The adduct 25a was alternatively synthesized by treating the product from acidic methanolysis of 2-pyrrolidone with DMAD under basic conditions (added solid sodium bicarbonate).…”

The Niecke Biradicals and Their Congeners – The Journey from Stable Biradicaloids to Their Utilization for the Design of Nonlinear Optical Properties

“…Of the series, the 1,3‐diazetine, 6 is yet experimentally unknown, but computationally (R = H) well characterized since 1980 . In comparison with, the corresponding 1,2‐diazetines were experimentally described . Next, in 2004 the synthesis of the corresponding germanium, 8 , and tin analogues, 9 , were reported by the groups of Power and of Lappert .…”