3907-03-7Relevant academic research and scientific papers
Amplification of the chiroptical response of UV-Transparent amines and alcohols by: N-phthalimide derivatization enabling absolute configuration determination through ECD computational analysis
Belviso, Sandra,Mazzeo, Giuseppe,Padula, Daniele,Santoro, Ernesto,Scafato, Patrizia,Superchi, Stefano
, p. 2094 - 2102 (2020/03/27)
The stereoselective transformation of chiral UV-Transparent amines and alcohols to phthalimides has proved to be a simple and efficient method to enhance the chiroptical response of these substrates allowing their reliable absolute configuration determination by computational analysis of ECD spectra. Such a transformation also leads to a significant reduction in the molecular conformational flexibility thus simplifying the conformational analysis required by the computational treatment. The method described herein thus allows the absolute configuration assignment to these challenging substrates to be much easier and reliable.
Practical synthesis of dirhodium(II) tetrakis[N-phthaloyl-(S)- tertleucinate]
Tsutsui, Hideyuki,Abe, Takumi,Nakamura, Seiichi,Anada, Masahiro,Hashimoto, Shunichi
, p. 1366 - 1368 (2007/10/03)
An efficient and reliable procedure for the preparation of dirhodium(II) tetrakis[N-phthaloyl-(S)-tert-leucinate], Rh2(S-PTTL)4, a universally effective catalyst for a range of enantioselective carbene transformations, is described. The N-phthaloylation of (S)-tert-leucine by the method of Bose with essentially no racemization is a key to this process.
Photochemistry of N-Phthaloyl α-Amino Acid Esters: A New Approach to β,γ-Unsaturated α-Amino Acid, Dihydrobenzazepinedione, and Pyrrolizidinone Derivatives
Griesbeck, Axel G.,Mauder, Harald,Mueller, Ingrid
, p. 2467 - 2476 (2007/10/02)
The N-phthaloyl-α-amino acid methyl esters of 2-aminobutyric acid (2a), valine (2b), norvaline (2c), tert-leucine (2d), isoleucine (2e), allo-isoleucine (2f), leucine (2g), methionine (2h), alanine (2i), and phenylalanine (2k) were synthesized in enantiomerically pure form via the N-phthaloyl-α-amino acids (1a-k), and their photochemistry was studied.Except 2i and 2k, which proved to be photostable, all compounds were converted into three types of products, depending on the substitution pattern: a) isomerization products (derivatives of β,γ-unsaturated α-amino acids) 3a, b, c, and e, b) ring expansion products (benzazepinedione esters) 4a and c, and c) cyclization products (5d from the tert-leucine derivative 2d).High diastereoselectivities (d.r. >95:5) were observed for all reactions except the transformations of the 2-aminobutyric acid derivative 2a.The absolute configuration of the α-stereogenic center was retained during photolysis, as proven for the isodehydrovaline (type a product) 3b.PCC oxidation (to give 7b) and hydrogenation afforded 2b with an optical rotation comparable to the starting material.Treatment of 3b with an acid or a base led to epimerization (3b') or isomerization of the C=C bond (6b), respectively.The diastereomeric dihydrobenzazepinedione esters 4a, b were formed with d.r. = 33:67 (cis:trans) and in 60percent yield during photolysis of 2a.The isoleucine derivative 2e, however, was converted into the cis isomer 4a with high diastereoselectivity (d.r. >95:5), whereas the corresponding allo substrate 2f was only converted into the trans-isomer 4b.Ethylene was extruded during irradiation of the latter substrates and during irradiation of the norvaline derivative 2c, whereas propene extrusion from the leucine derivative 2g led to the formation of the unsubstituted type b product 4c.The methionine derivative 1h was the only N-phthaloylamino acid which did not show photodecarboxylation, instead two ξ-hydrogen abstraction products were formed: the hydroxy acid 9h and the tetracylic lactone 10h.The methionine ester 2h was only converted into the ring expansion products 11h, h' presumably by a photo electron transfer step.The chronology of the double hydrogen transfer reaction (γ- followed by δ-H abstraction, leading to type a products) was determined by using the deuterium labeled compound (+/-)-2b.Key Words: Photochemistry / α-Amino acids / Amino acids, β,γ-unsaturated / Photoisomerization / Benzazepinedione esters / Selectivity, enantio-, diastereo-
