Synthesis of Unsaturated Amino Acids by [3,3]‐Sigmatropic Rearrangement of Chelate‐Bridged Glycine Ester Enolates

Abstract

number of isomeric forms which may differ considerably in strain and hence in energy content. [20] Among the theoretical methods used for the calculation of the heat of formation of C,,, MM3 and the incremental method give the best results (both providing values which are slightly lower than the experimental ones), whereas the number resulting from MNDO calculations is much higher. From these comparisorls it can he concluded that the first two methods mentioned are best suited for the prediction of the heat of forrnatioii of higher fullerenes. Due to the lack of availability of these carbon spheres in quantities large enough for experimental measurements, knowledge about their stability will have to rely on theoretical calculations for some time. Synthesis of Unsaturated Amino S. Suniier in ( ' o i i i h i i \ i i~i C"i

Recent advancements in the homoallylamine chemistry

“…Then, Barlett and co-workers investigated the diastereoselectivity of this process [56]. Nowadays, this methodology has been applied successfully for diastereoselective synthesis of other amino acids with β-quaternary carbon centers (Kazmaier's method) [57][58][59]. The rearrangement of amino acid allylic esters occurs in a high diastereoselective fashion due to enolate fixation by chelation.…”

Synthesis of Functionalized Alkylidenecyclopropanes by Ireland–Claisen Rearrangement of Cyclopropenylcarbinyl Esters

“…Related metalated cyclopropenes are known to undergo rapid ring cleavage to the corresponding metalated alkynyl malonates but can be trapped in situ with reactive electrophiles such as TMSCl. 21 Thus, the resulting silylcyclopropene 13 would undergo Ireland−Claisen rearrangement, through the silyl ketene acetal intermediate 14, to provide alkylidene-(silylcyclopropane) 15. Lowering the quantity of KHMDS (2 equiv) induced quantitative silylation of cyclopropene 12 but resulted in an incomplete Ireland−Claisen rearrangement of 13, thereby confirming that silylation of 12 precedes the [3,3]-sigmatropic rearrangement.…”

Stereoselective terminal functionalization of small peptides for catalytic asymmetric synthesis of unnatural peptides

“…The direct introduction of side chains to a peptide backbone represents an attractive method for the preparation of various unnatural peptides. Achiral glycine subunit has generally been used for this purpose (3), and glycine enolates (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), glycine radicals (15)(16)(17)(18), and glycine cation equivalents (19)(20)(21)(22) have been exploited as reactive intermediates. However, the control of the stereochemical outcome of these processes in an absolute sense is a difficult task, especially in the modification of linear peptides, and hence development of an efficient and practical approach to establish sufficient stereoselectivity and general applicability has been eagerly awaited (12,23,24).…”