β-Lactams from ester enolates and silylimines: An enantiospecific synthesis of monocyclic β-lactams.

Synthesis and Use ofN-(Trimethylsilyl)imines

“…A further useful application of this approach to optically active azetidinones is illustrated by the enantioselective synthesis of the 3-amido-4-alkylazetidinones, including the commercially available Aztreonam, 81 via addition of the lithium enolate of the STABASE, a cyclic silyl-protected form of the glycine ester, 82 to the N-(trimethylsilyl)imine of lactaldehyde. 83 Once again a very high trans diastereoselectivity has been observed. In this case, in order to obtain the natural (R) configuration on the C-3 stereocenter, the (R)-lactaldehyde must be used (Scheme 27).…”

“…By using scalemic N -(trimethylsilyl)imines derived from α-hydroxy aldehydes, the syntheses of carbapenem antibiotics PS-5, PS-6, and β-methyl-PS-5 , have been achieved (Scheme ). A further useful application of this approach to optically active azetidinones is illustrated by the enantioselective synthesis of the 3-amido-4-alkylazetidinones, including the commercially available Aztreonam, via addition of the lithium enolate of the STABASE, a cyclic silyl-protected form of the glycine ester, to the N- (trimethylsilyl)imine of lactaldehyde . Once again a very high trans diastereoselectivity has been observed.…”

Synthesis of NH -3-phenylsulfanyl- and NH -3-benzylsulfanyl-azetidinones from 1-phenylsulfanyl- or 1-benzylsulfanyl-3-aza-1,3-dienes

“…(2) The compound A 1 , belonging to group A and compound B 1 , belonging to group B (Scheme 2), have been elaborated to the same enantiomeric pure compound (epc) C and, subsequently, to Aztreonam of known configuration and optical activity. 26,13 By this way, and taking into account that the parent compound of A 1 was the (S)-lactaldehyde, the parent compound of B 1 was the (R)-lactaldehyde and that the trans relationship between H 3 and H 4 is not in discussion (J¼2. 5 Hz), the absolute configuration of A 1 and B 1 is so far established.…”

“…To a hexane solution of 1 mmol of [3-methyl-2-(S)-(triisopropyl-silanyloxy)-butylidene]-(trimethyl-silanyl)-amine (2d), 26 prepared according to a literature procedure, 24 were added, dropwise, at 08C, under efficient stirring, TEA (2 mmol, 280 mL)) followed by a hexane solution of commercially available phenylsulfanylacetyl chloride (3) (1 mmol, 148 mL). The solution was stirred at 08C for 40 min and then for 1 h at rt.…”