Stereoselective synthesis of β-substituted aspartic acids via tetrahydro-1,3-oxazin-6-ones

Diastereoselective Synthesis of α-Methyl and α-Hydroxy-β-Amino Acids via 4-Substituted-1,3-Oxazinan-6-ones

“…All alkylations performed provided the trans - 10 and cis - 11 products (Scheme , Table ). Alkylation using LDA (entry 1) or LiHMDS (entry 2) as base provided selectivity similar to the results observed by Burtin et al , However, NaHMDS (entry 3) and KHMDS (entry 4) both afforded significantly better selectivity. This trend in the results suggests the anion is less important than the metal counterion.…”

“…However, to better utilize 1,3-oxazinan-6-ones in the efficient production of α,β-disubstituted-β-amino acids, the yields of the oxazinanones 3 − 9 (30−45%) (Scheme ) we reported 17 using the procedure of Ben-Ishai needed to be improved . Several other methods were attempted without any improvement in yield until the conditions of Burtin et al , were applied. It was found that stirring the N -protected β-amino acids in toluene, with a catalytic amount of acid and activated 4 Å molecular sieves at 90 °C for 3−4 h, resulted in a marked improvement in yields of the oxazinanones 3 − 9 (65−78%).…”

“…1,3-Oxazinan-6-one 5-Alkylation. Burtin et al , is the only group to have prepared 5-alkyl-1,3-oxazinan-6-ones. The oxazinanones were derived from an N -Boc-protected aspartic acid derived residue; thus two acidic protons were present, requiring 2 equiv of base to form enolates.…”

“…The addition of hexamethylphosphoramide (HMPA) to enolate reactions had varying effects on reaction yields and stereoselectivity. Burtin et al , observed that the addition of HMPA to the α-alkylation of oxazinanones did not affect the stereochemical outcome of the reaction. In their hands, the addition of HMPA resulted only in lower yields of the desired products.…”

Chemo- and Stereospecific Solid-State Thermal Dimerization of Sodium trans-2-Butenoate and γ-Ray-Induced Single-Crystal-to-Single-Crystal Dimerization of Hexaaquamagnesium trans-2-Butenoate Dihydrate: Both Give rel-(3S,4R)-1-Hexene-3,4-dicarboxylate but by Different Mechanisms. Stereospecific γ-Ray-Induced Trimerization of Sodium trans-2-Butenoate

“…While there are only a few structural analogues for the 98.5°and 175.9°t orsion angles, the two different values appear to represent the expected values for each "end" of the disordered product. The major isomer is near to values observed for unsaturated analogues 29 LISVUG (124°), 59 LISWAN (−129°), 59 and LISWIV (−122°), 59 while the minor isomer value is in good agreement with the saturated analogues JOKJOI (177°), 60 KAGJUX (161°), 61 and VODFOJ (−174°). 62 Examination of Tables 1A and 1B reveals some interesting observations.…”