(R)- or (S)-4-(3-hydroxy-4,4-dimethyl-2-oxopyrrolidin-1-yl)benzoic acid as a new chiral auxiliary for solid phase asymmetric Diels–Alder reactions (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)
Highly Diastereoselective Diels−Alder Reaction Using a Chiral Auxiliary Derived from Levoglucosenone
Organic Letters, 2005
A new chiral auxiliary derived from levoglucosenone is reported. The compound is obtained by a cycloaddition reaction with 9-methoxy methylanthracene followed by a diastereoselective reduction of the C-2 keto function. The auxiliary has been used as a chiral template in an asymmetric Diels−Alder reaction of the corresponding acrylic ester derivative with cyclopentadiene. The results showed excellent diastereomeric excess even at room temperature when the reaction was promoted by Et 2 AlCl as the Lewis acid.
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
Tetrahedron Letters, 1983
The Lewis-acid promoted Diels-Alder reaction of the allenic ester 10 provides the adduct 11 with excellent a-facial selection leading to an efficient enantioselective synthesis of (-)-i3-santalene and to the recovery of the chiral control element 7. Asymmetric Diels-Alder reactions using chiral dienophiles or dienes have received a great deal of attention over the last few years [21 . Thus, almost quantitative diastereoface differentiation has been achieved in the acrylate/ cyclopentadiene addition 1 + 2 as recently reported by this laboratory [31 --(Scheme 1). Scheme 1 , CHzCI, TiC12(0iPr),t-20' 96% si -attack 99.3Kd.e.%$!= y 1 2 The easy accessibility of the rationally designed, recoverable, camphorderived control element, together with its predictable and efficient topological bias, offers attractive possibilities for the synthesis of chiral natural products. 4665
Clay-catalysed asymmetric Diels-Alder reaction of cyclopentadiene with chiral acrylates
1993
Clay-catalysed Die&&l&r reactions of cyclopentadiene with several chiral acrylates are studied. The results obtained show that these solids are not efficient catal sts when chiraI auxikies of large size are used. Clay-catalysed reactions between cyclopen tar5ene and (Rf-O-~loy~~~~~ are compared with non-catalysed and IX!4 and ~U2~~y~ reactioos. With regard to diastem&ciaI selectivity, the clays studied behave like homogeneous ~~~~ catalysts. Clay-catalysed reactions of (R)-O-acryloylpantoIactone lead to the (lS,2S,4S)cycloadduct with good chemical yield, high % d.e. and excel&m endokxo se&My. Given that (-)-menthyl acrylate leads to the (lR,2R,4R)-cycioadduct with about the same pi@ereofacial selectivity, (-)-menthol and (IV-pantolactone behave as complementary chiral aux&a~, The Diels-Alder reaction of acrylic acid derivatives is an important reaction since the cycloadducts obtained are key intermediates for the total synthesis of a variety of natural productsl. Excellent diastereofacial sekctivities have been o&a&d in asymmetric Die&A&r iuactions of pm&ml 1,3-dienes with chiral auyIates.2
Tetrahedron, 2009
Chiral alcohols were designed and easily prepared from levoglucosenone, a biomass-derived valuable synthon. These alcohols were tested as chiral auxiliaries in asymmetric Diels-Alder reactions between the corresponding acrylates with acyclic and cyclic dienes. The regio, stereo, and facial selectivity varied from very good to excellent, depending upon the benzylic substitution of the auxiliary and the diene employed. As a consequence, after removal of the auxiliary, the resulting carboxylic acid derivatives were obtained in 72-99% ee. 748 cm À1 ; 1 H NMR (CDCl 3 ) d 7.44-7.05 (m, 8H, aromatic), 6.36 (dd, J 4 0 -5 0 ¼J 5 0 -6 0 ¼7.0 Hz, 1H, H-5 0 ), 6.28 (dd, J 5 0 -6 0 ¼J 6 0 -7 0 ¼7.0 Hz, 1H, H-6 0 ), 4.99 (d, J 1-2 ¼3.3 Hz, 1H, H-1), 4.58 (d, J 5-6exo ¼4.4 Hz, 1H, H-5), 4.26-4. , 4.13 (s, 1H, H-4a), 3.67 (dd, J gem ¼7.2 Hz, J 5-6exo ¼4.4 Hz, 1H, H-6exo), 3.63 (d, J gem ¼7.2 Hz, 1H, H-6endo), 3.59 (s, 3H, H-8), 3.01 (br s,1H, H-7 0 ), 2.68 (td, J 2 0 -3 0 exo ¼9.9 Hz, J 2 0 -3 0 endo ¼5.5 Hz, J 2 0 -7 0 ¼2.2 Hz, 1H, H-2 0 ), 2.60 (br s, 1H, H-4 0 ), 2.35 (dd, J 3-4 ¼10.4 Hz, J 2-3 ¼6.0 Hz, 1H, H-3), 2.10 (d, J 3-4 ¼10.4 Hz, 1H, H-4), 1.79 (td, J gem ¼12.9 Hz, J 2 0 -3 0 exo ¼9.9 Hz, J 3 0 exo-4 0 ¼2.6 Hz, 1H, H-3 0 exo), 1.66 (td, J gem ¼12.9 Hz, J 2 0 -3 0 endo ¼5.5 Hz, J 3 0 endo-4 0 ¼2.8 Hz, 1H, H-3 0 endo),
Tetrahedron: Asymmetry, 1994
Eiaaatiopure I-methoxy-3-(l-phenyl-aad 2-phenyl-2-hydroxyethylsulfinyl)-13-buta were prepared from ethyl mat&late. D&Alder reactions with methyl aaylate proceeded with complete regioselectivity and high diastereosekctivity. Diels-Alder reactions of acrylic acid derivatives have provided key intermediates for natural product synthesis. 1 For purposes of asymmetric synthesis high diastereofacial selectivities have been obtained in cycloadditions of prochiral 1,3-dienes with chiral acrylates,2 but the combination of enantiopure dienes with prochiral acrylates has received less attention ,3,4 despite its potential advantages in extending the scope and usefulness of these asymmetric cycloadditions. Recently we reported that lithium perchlorate-catalysed cycloaddition of methyl acrylate to the enantiopure 1-methoxy-3-alkylsulfinyl-1,3-butadienes 4 was controlled separated PhCH signals in CgDg. The assignment of absolute stereochemistry for the various Diels-Alder adducts is based on conqwison of 'H NMR data and the established relationship betwceu cbirality at sulfur and diastereofacial selectivity (ref. 4).
2,5-Diketopiperazines, new chiral auxiliaries for asymmetric Diels-Alder reactions
Tetrahedron Letters, 1997
Diketopiperazines have been utilized as chiral auxiliaries for asymetric Diels-Alder reactions. Cyclo-Sphenylalanyl-R-proline (2) was found to be the most promising of these auxiliaries and afforded Diels-Alder adducts in high chemical yield (78 -95%), with endo selectivities generally greater than 9:1. The diastereoselectivities observed were comparable to the best previously published values. © 1997 Elsevier Science Ltd.