New diastereoselective method for constructing a carbon chain by conversion of N,N′-dialkyl-N,N′-diacylhydrazines to threo-1,2-dicarboxylic acid derivatives

A Cascade Process of Hydroxamates Renders 1,6-Dioxa-3,9-diazaspiro[4.4]nonane-2,8-diones

“…Crystal structure of (4S,5R,7R)-9-benzyl-3,4-dimethyl-7-phenyl-1,6-dioxa-3,9-diazaspiro [4,4]nonane-2,8-dione (6b) (see the Supporting Information)…”

“…structure analysis of the same compound generated from the double cyclization of (R)-2-(benzylamino)-2-oxo-1phenylethyl (S)-2-[(tert-butoxycarbonyl)(methyl)amino]propanoate (Figure 1). 15 Figure 1 Crystal structure of (4S,5R,7R)-9-benzyl-3,4-dimethyl-7-phenyl-1,6-dioxa-3,9-diazaspiro [4,4]nonane-2,8-dione (6b) (see the Supporting Information) Identification of the second diastereomer was not possible, as it was separated either as a mixture of two diastereomers or as a liquid diastereomer, which was obtained in insufficient quantity for a 2D NMR experiment (i.e., a NOESY experiment). Nevertheless, determination of the ratio was carried out by using the integral ratio of diagnostic signals in the 1 H NMR spectrum of the crude mixture.…”

“…The reaction was maintained at -78 °C for about 15-20 min while stirring vigorously and was then removed from the dry ice bath and allowed to stir at room temperature for an additional 13-14 h. After the reaction was deemed complete (via TLC), the solvent was evaporated under reduced pressure and the crude product was then applied directly to a silica gel column and eluted with the appropriate solvent system. 9-Benzyl-3-methyl-7-phenyl-1,6-dioxa-3,9-diazaspiro [4,4]nonane-2,8-dione (6a, 7a) Prepared using 4a (0.46 mmol, 0.19 g), TBSOTf (1.15 mmol, 0.31 mL) and Et 3 N (1.15 mmol, 0.16 mL) in accordance with GP3.…”

“…The more polar isomer 7a 15 was isolated as a mixture of two diastereomers. 1 H NMR (400 MHz, CDCl 9-Benzyl-3,4-dimethyl-7-phenyl-1,6-dioxa-3,9-diazaspiro [4,4]nonane-2,8-dione (6b, 7b) Prepared using 4b (0.47 mmol, 0.20 g), TBSOTf (1.2 mmol, 0.31 mL) and Et 3 N (1.2 mmol, 0.16 mL) in accordance with GP3.…”

“…In fact, only a few studies have focused on this subject (Scheme 1). [4][5][6][7][8][9][10][11] Conventional methods for enolate coupling typically use a strong base followed by metal salts such as Cu(OAc) 2 or Ti-Cl 4 . However, these harsh conditions often result in poor yields and diastereoselectivities and limit the range of substrates.…”