Diastereoselective Conjugate Reduction and Enolate Trapping with Glyoxylate Imines. A Concise Approach to β-Lactams that Involves a Ternary Combination of Components
“…Aminolactone 132 was smoothly obtained by oxidation of the lactol 131 with a chromium(VI) reagent (Scheme 48). 42 Synthesis of the natural compound amicoumacin C 138 has been described. 43 Condensation of benzyl bis(trifluoroethyl) phosphonoacetate with 4-oxoazetidine-2-carbaldehyde 133 was achieved using potassium carbonate in the presence of 18-crown-6 and gave the corresponding (Z)-benzyl ester together with its (E)-isomer, ratio ca.…”
Section: Monocyclic Five-membered Ringsmentioning
confidence: 99%
“…Ring opening of β-lactam 130 with a Grignard reagent led to the corresponding β-amino ketone, which after l -Selectride reduction provided aminolactol 131 . Aminolactone 132 was smoothly obtained by oxidation of the lactol 131 with a chromium(VI) reagent (Scheme ) 48 49 …”
“…Aminolactone 132 was smoothly obtained by oxidation of the lactol 131 with a chromium(VI) reagent (Scheme 48). 42 Synthesis of the natural compound amicoumacin C 138 has been described. 43 Condensation of benzyl bis(trifluoroethyl) phosphonoacetate with 4-oxoazetidine-2-carbaldehyde 133 was achieved using potassium carbonate in the presence of 18-crown-6 and gave the corresponding (Z)-benzyl ester together with its (E)-isomer, ratio ca.…”
Section: Monocyclic Five-membered Ringsmentioning
confidence: 99%
“…Ring opening of β-lactam 130 with a Grignard reagent led to the corresponding β-amino ketone, which after l -Selectride reduction provided aminolactol 131 . Aminolactone 132 was smoothly obtained by oxidation of the lactol 131 with a chromium(VI) reagent (Scheme ) 48 49 …”
“…In contrast, most of reductive Mannich-type reactions using imines and α,β-unsaturated carbonyl compounds gave β-amino esters, but there are only a few reports for a direct synthesis of β-lactams by reductive Mannich-type reactions [ 14 , 18 – 21 ]. We recently reported a reductive Mannich-type reaction using a combination of RhCl(PPh 3 ) 3 and Et 2 Zn to give the corresponding syn -β-lactams from α,β-unsaturated esters and imines in good to excellent yields together with a small amount of the β-amino esters ( Scheme 1 ) [ 22 – 23 ].…”
SummaryAn effective synthesis for syn-β-lactams was achieved using a Rh-catalyzed reductive Mannich-type reaction. A rhodium–hydride complex (Rh–H) derived from diethylzinc (Et2Zn) and a Rh catalyst was used for the 1,4-reduction of an α,β-unsaturated ester to give a Reformatsky-type reagent, which in turn, reacted with an imine to give the syn-β-lactam. Additionally, the reaction was applied to the synthesis of (±)-ezetimibe, a potent β-lactamic cholesterol absorption inhibitor.
“…The combined extracts were dried over Na 2 SO 4 . The organic phase was concentrated under reduced pressure, and the resultant residue was purified by neutral silica gel column chromatography (eluent: hexane:EtOAc = 15:1), to give the desired product (5).…”
Highly practical synthetic methods were developed for the C- and N-selective Grignard addition reactions of N-4-MeOC6H4-protected α-aldimino esters in the presence or absence of zinc(II) chloride. Diastereoselective C-alkyl addition, tandem C-alkyl addition-N-alkylation, and some transformations to synthetically useful optically active azacycles were demonstrated.
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