Mild Synthesis of α-Oxoketene O.N-Acetals from β-Oxothioxo Esters and Amines

Carbohydrate α-oxoketene N,O-ketals in the synthesis of dihydroquinolines

“…The crude product (13.9 g) was purified by crystallization from dichloromethane-hexane to yield, after drying (45 ЊC, 4 mbar, 1 h), enone 1 (10.0 (8), 141 (11), 131 (33), 105 (100) and 77 (22). Ϫ1 3240, 3200, 2923, 2854, 1631, 1600, 1547, 1450, 1376, 1104, 753 (16).…”

“…10,11 α-Oxoketene O,O- 12 and N,O-ketals were used to a lesser extent. [13][14][15][16] Various representatives of this class, such as aminosubstituted chromones, have been found to be of interest in a pharmaceutical context. 17, 18 Carbohydrate α-oxoketene N,Oketals have not been reported yet with the exception of the mention of a furanose derivative (1-amino-1-deoxy--threohex-1-enofuranos-3-ulose) which was not described in detail.…”

Preparation of 1,6‐naphthyridine‐2,5(1H,6H)‐diones

“…For example, N-propyl-3-oxobutanamide 3b afforded 2b in 59% yield. Table 1 Synthesis of 3-Acyl-1,6-dialkyl-7-methyl-1,6-naphthyridine-2,5(1H,6H)-diones (2) from α-Oxoketene O,N-acetals (1) 1,6-Naphthyridine-2,5(1H,6H)-diones are rare compounds in the literature, and there are only few reports dealing with their preparation [5]. For example, 1,6-dimethyl-1,6-naphthyridine-2,5(1H,6H)-dione was synthesized by the Skraup reaction, alkylation, and then oxidation, [6] while the reaction of ethyl N-benzylacetimidate with diketene was demonstrated to give 1,6-naphthyridine-2,5(1H,6H)-diones in moderate yields [7].…”

“…Commercially available compounds were used without purification. 2-Acyl-1-alkylamino-1-ethoxyethylenes (1) [1] and N-alkyl-3-oxobutanamides (3) [4,12] were prepared according to literature methods.…”