Derivate des tetrameren Kohlenmonoxids

Synthesis and reactivity of compounds with cyclobutane ring(s). 10. Syntheses of squaric acid, its monoorthoesters, and related derivatives via [2 + 2] cycloadditions of tetraalkoxyethylenes with heterosubstituted ketenes

“…Treatment of 6.96 g (0.02 mol) of crude 4d with silica gel/3% Et3N according to the general procedure for conversion of, e.g., 4a to 5a (see above) yielded 1.4 g (50%) of 8: mp 55.5-56 °C (methanol/hexane) (lit. mp 5631 and 52-53 °C32); NMR (CDC13) 4.36 (s, 6 H, two OCH3); indistinguishable from a sample of the authentic material (IR, TLC in two solvent systems) prepared from squaric acid and methanol.31 Ethyl 3-Phthalimido-4,4,4-triethoxy-(Z)-2-butenoate (11) and 1.1.1.4.4.4-Hexaethoxy-2-phthalimido-(Z)-2-butene (12). A solution of 11.6 g (0.02 mol) of 4h in 300 mL of dry ethanol was kept at room temperature for 24 h. After the alcohol was evaporated, the residue was subjected to column chromatography.…”

“…l-(Methoxyacetoxy)-2-methoxy-3,3,4,4-butoxy-l-cyclobutene (4b). Similarly, from 0.1 mol of tetrabutoxyethylene (lc)2 was obtained an oil, which, after being placed under vacuum (0.5 mm/80 °C) for 6 h, provided 19.8 g (86%) of 4b (NMR purity was better than 95%): IR (neat) 1783,1730,1292,1200 cm'1; NMR (CDC13) 0.98 (br t, 12 H, four CH3), 1.1-1.9 (m, 16 H, four-CH2CH2-), 3 -3.9 (m, 8 H, four -OCH2-), 3.48 (s, 3 H, -OCH3), 3.83 (s, 2 H, -C0CH20-), 4.16 [s, 3 H, OCH3-C(2)]). Anal.…”

“…l-(Acetoxyacetoxy)-2-acetoxy-3,3,4,4-tetramethoxy-l-cyclobutene (4d). From 0.138 mol of tetramethoxyethylene (la) and 0.3 mol of acetoxyacetyl chloride was obtained an oil which, when placed under vacuum (0.1 mm/60 °C) for 4 h, gave 38.9 g (82%) of crude 4d (purity assessed from NMR was about 94%): IR (neat) 1786, 1757, 1724,1085 cm'1; NMR (CDC13) 2.18, 2.21 (two s, 6 H, two -COCH3), 3.50 (s, 12 H, four -OCH3), 4.73 (s, 2 H, -C0CH20-).…”

“…From 0.1 mol of lb and 0.21 mol of (methylthio) acetyl chloride22 was obtained 35.2 g of an oil consisting of 66% 4g, 18% 5g, about 13% ethyl (methylthio)acetate, and a small amount of unidentified byproducts. Assignment of NMR (CDC13) signals for 4g: 1.28 (t, J = 8.5 Hz, 12 H, four CH3), 2.33, 2.42 (two s, 6 H, two SCH3), 3.27 (s, 2 H, -COCH,S-), 3.S-3.9 (m, 8 H, four -OCH2-). For 5g: 1.26 (t, J = 8.5 Hz, 6 H, two CH3), 1.48 (t, 3 H, CH3), 2.55 (s, 3 H, SCH3), 3.5-3.9 [m, 4 H, (-OCH2)2-C(4)], 4.5 [q, J = 8.5 Hz, 2 H, (-OCH2-)-C(3)].…”