Endo-benzonorbornen-2-ol as an efficient non-natural chiral auxiliary in the asymmetric aza-Diels-Alder reactions between cyclopentadiene and (1-phenylethyl)iminoacetates (original) (raw)
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European Journal of Organic Chemistry, 2007
The acrylate derivative of the (R)‐4‐(3‐hydroxy‐4,4‐dimethyl‐2‐oxopyrrolidin‐1‐yl)benzoic acid benzyl ester (R)‐2 reacted with 1‐(benzyloxycarbonylamino)cyclohexadiene 3 under microwave irradation in solvent‐free conditions to yield [4+2] cycloadducts in good yields (91 %). The reaction proceeded with moderate endo selectivity (67 %) and good facial selectivity (90 %). The major cycloadducts were isolated and transformed to afford three enantiopure bicyclic β‐amino acids: (1S,2R,4R)‐1‐(benzyloxycarbonylamino)bicyclo[2.2.2]oct‐5‐ene‐2‐carboxylic acid [(1S,2R,4R)‐4], (1R,2R,4S)‐1‐(benzyloxycarbonylamino)bicyclo[2.2.2]oct‐5‐ene‐2‐carboxylic acid [(1R,2R,4S)‐5] and (R)‐1‐aminobicyclo[2.2.2]octane‐2‐carboxylic acid [(R)‐6]. This work has led to the preparation of these enantiopure bicyclic β‐amino acids and provides a rare example of an asymmetric Diels–Alder reaction by microwave activation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Asymmetric Diels-Alder reactions of chiral (E)-2-cyanocinnamates with cyclopentadiene
The Journal of Organic Chemistry, 1992
High and complementary diastereoselectivities were obtained in the asymmetric Diels-Alder reactions of chiral (E)-2-cyanocinnamates with butadiene when (SI-ethyl lactate and (R)-pantolactone were used as chiral auxiliaries in the presence of TiC14. The most selective reactions allowed the synthesis of the cycloadducts 2a and 3b, whose absolute configurations were assigned by a n X-ray diffraction study of diastereoisomer 3b. The hydrolysis and subsequent hydrogenation of the stereoisomers gave the corresponding enantiomeric cyanocarboxylic acids. From these products the four 1-amino-2-phenyl-1-cyclohexanecarboxylic acids were synthesized in enantiomerically pure form following a protocol with stereocontrolled and stereodivergent transformations. Cativiela, C.; Dfaz-de-Villegas, M. D.; Mayoral, J. A.; Peregrina, J. M. Tetrahedron 1993, 49, 677. (b) Avenoza, A.; Cativiela, C.; Diaz-de-Villegas, M. D.; Peregrina, J. M. Tetrahedron 1993,49, 10987. (4) (a) Avenoza, A.; Cativiela, C.; Mayoral, J. A.; Peregrina, J. M.; Sinou, D. Tetrahedron: Asymmetry 1990, I, 765. (b) Avenoza, A.; Cativiela, C.; Mayoral, J. A.; Peregrina, J. M. Tetrahedron: Asymmetry 1992, 3, 913. (c) Avenoza, A.; Cativiela, C.; Gimeno, S.; Lahoz, F. J.; Mayoral, J. A.; Peregrina, J. M. J. Org. Chem. 1992, 57, 4664. 0022-3263/94/1959-7774$04.50/0 synthesis of chiral products containing quaternary carbon atoms and also that (8)-ethyl lactate and (R)-pantolactone are excellent and complementary chiral auxiliaries.
Tetrahedron: Asymmetry, 2004
The synthesis of enantiopure (R)-and (S)-4-(3-hydroxy-4,4-dimethyl-2-oxopyrrolidin-1-yl)benzoic acid is described and the corresponding supported chiral acrylate derivative has been used as a dienophile in solid phase asymmetric Diels-Alder reactions with different dienes. In all cases, the reaction gave the expected compound in good yield and with high regio or endo selectivity. Moreover, a high facial diastereoselectivity (86-99% de) was obtained using 2,3-dimethylbutadiene, cyclopentadiene or 1,3-cyclohexadiene. In contrast, low to moderate facial diastereoselectivity (40-76% de) was observed with isoprene depending on the polymer used.
New carbohydrate-based chiral auxiliaries in Diels–Alder reaction
Tetrahedron-asymmetry, 1998
The carbohydrate derivatives 1–5 were evaluated as chiral auxiliaries in the Diels–Alder reaction of its acrylate derivatives 6a–e with cyclopentadiene promoted by Lewis acids. Although excellent endo:exo ratios (98:2) were obtained in many cases, the π-facial selectivities were from low to moderate (up to 60% d.e.). An effect of non-coordinating solvents reversing the stereoselectivities of adducts obtained from acrylates 6a,b
ARKIVOC, 2002
Benzyl 2H-azirine-3-carboxylate 1b added as a dienophile to several cyclic and acyclic conjugated dienes at room temperature to give derivatives of the 1-azabicyclo[4.1.0]hept-3-ene ring system. The cycloaddition reactions gave exclusively the products of endo addition with respect to the three membered ring, as shown by crystal structures of two of the compounds, 4c and 4d. Methods for the cis-hydroxylation of the double bonds of some of these compounds were explored and four dihydroxy compounds were isolated from the adducts with cyclohexa-1,3diene, 1-acetoxybutadiene, 1,4-diacetoxybutadiene and 1,4-bis(tertbutyldimethylsilyloxy)butadiene, in each case as single isomers. The structure of one of these, compound 6, was supported by an X-ray crystal structure determination. Methods for reduction of the benzyloxycarbonyl group to a hydroxymethyl group were also investigated with the aim of forming novel glycosidase inhibitors analogous to nojirimycin.
Chirality, 2019
Enantiopure 3-((R)-and 3-((S)-1-phenylethyl)-4-oxazoline-2-ones were evaluated as chiral building blocks for the divergent construction of heterocycles with stereogenic quaternary centers. The N-(R)-or N-(S)-1-phenylethyl group of these compounds proved to be an efficient chiral auxiliary for the asymmetric induction of the 4-and 5-positions of the 4-oxazolin-2-one ring through thermal and MW-promoted nucleophilic conjugated addition to Michael acceptors and alkyl halides. The resulting adducts were transformed via a cascade process into fused six-membered carbo-and heterocycles. The structure of the reaction products depended on the electrophiles and reaction conditions used. Alternative isomeric 4-methylene-2-oxazolidinones served as chiral precursors for a versatile and divergent approach to highly substituted cyclic carbamates. DFT quantum calculations showed that the formation of bicyclic pyranyl compounds was generated by a diastereoselective concerted hetero-Diels-Alder cycloaddition. KEYWORDS (R)-and (S)-1-phenylethylamine, 4-methylene-2-oxazolidinones, 4-oxazolin-2-ones, hetero-Diels-Alder reaction, microwave irradiation 1 | INTRODUCTION Chiral 1,3-oxazolidin-2-ones have been widely used as efficient auxiliaries for the asymmetric synthesis of a large variety of enantiopure and highly functionalized carbonylic compounds. 1-9 Likewise, the preparation of α-amino alcohols and α-amino acids has been designed based on the approach of the transformation of chiral 1,3-oxazolidin-2-ones, 10-13 which in turn can be obtained from optically pure α-amino alcohols 10 and α-amino acids, among other substrates. 1-9 The synthetic applicability of these heterocycles has increased with the development of new methods for their construction. 14-21 Functionalized 4-methylene-1,3-oxazolidin-2-ones have