1-acetylvinyl acrylates: new captodative olefins bearing an internal probe for the evaluation of the relative reactivity of captodative against electron-deficient double bonds in Diels-Alder and Friedel-Crafts reactions (original) (raw)
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European Journal of Organic Chemistry, 2007
Captodative olefins 1-acetylvinyl carboxylates substituted with alkyl groups at the β position, 12, strongly modified the regioselectivity of 1,3-dipolar cycloadditions with respect to the behavior observed for their unsubstituted analogs, 1. When the reaction of 12 was carried out with diphenyl nitrone (7a), the corresponding C-4 disubstituted isoxazolidines were obtained as a mixture or as single stereoisomers, in contrast to the isomeric C-5 disubstituted heterocycles yielded by olefins 1. Nevertheless, olefins 12 reacted with benzonitrile oxide (2a) to give the C-5 acetyl isoxazoles, as [a] We have also assessed the perturbation effect of a third substituent at the β position of the double bond of 1 on the reactivity, regio-, and stereoselectivity of these olefins in Diels-Alder reactions. We prepared β-functionalized 1acetylvinyl arenecarboxylates 9; however, they failed to react with cyclopentadiene (10) and isoprene (11), except for β-brominated olefin 9a, which undergoes addition to these dienes to give the exo and para adducts, respectively, as the major isomers (Scheme 3). [12a] The ratio of regioisomers obtained with diene 11, under thermal conditions, was similar to that observed for unsubstituted olefin 1a. The low reactivity of dienophiles 9b and 9c can be ascribed to efficient delocalization of the electron lone pair of the heteroatom of the β-substituent towards the double bond.
Chemistry - A European Journal, 2002
Experimental conditions for the intramolecular cycloaddition of four related pentadienyl acrylates 3, 4, 5 and 6 are reported. In contrast with several previous reports, pentadienyl acrylates do undergo synthetically useful intramolecular Diels ± Alder reactions: 3, 4, 5 and 6 cyclise at reasonable rates at temperatures of 132 ± 180 8C at atmospheric pressure in moderate to good yields. The stereochemical outcome of each of these reactions was accurately measured and the results are in good agreement with transition structure populations predicted using B3LYP/6-31G(d) theory. The parent system 3 cyclises with moderate endo selectivity; the presence of either a C5-methyl substituent or a C3-bromine atom results in a slight shift towards the trans-fused exo stereoisomer but-overall-a less selective reaction. The presence of both C3-Br and C5-CH 3 substituents results in a marked improvement in stereoselectivity with the exo,lk-product predominating. Interpretation of B3LYP/6-31G(d) transition structures allows insights into the improvement in stereoselectivity obtained by incorporating a removable ™steric directing group∫ into a 5-methyl-1,3,8-nonatriene precursor.
ChemInform, 1999
A correlation between the solvent polarity and the logarithm of the diastereoisomer ratio (dr) was found for the uncatalyzed [4 2] cycloaddition of cyclopentadiene to N,N'-fumaroyldi[(2R )-bornane-10,2-sultam]. Using the Abboud-Abraham-Kamlet-Taft parameters, predictive values for this method, allowed an optimum diastereoisomeric excess (de) of 96% ( EtOH, À 788). A similar diastereoselectivity was achieved using 5m LiClO 4 /Et 2 O or H 2 O/b-cyclodextrin, and the influence of supercritical CO 2 is also reported. Selective cycloadditions of apolar diene in polar solvents are entropically favored by the greater dipole moment of the Nenoylcamphorsultam syn-s-cis conformers and of the C(a)-re transition states. Implications on the stereochemical course of the reaction are discussed.
Tetrahedron, 1994
The Diels-Alder cycloadditions of methyl acrylate to the unsymmetrical hexacyclo[ 10.2.1.0a~tt.ti~9.~~t4.09~t3]pentadecadienes lb-f proceed with a high degree of n-facial stereoselectivity but only moderate regioselectivity. The results of fixed model transition state calculations, performed in an effort to establish the factors which control selectivity in these cycloadditions, are reported. INTRODUCTION Recent efforts in our laboratories have been concerned with (i) studies of x-facial selectivity in Diels-Alder reactions to facially differentiated 1,3-cyclohexadienest and (ii) the synthesis and chemistry of novel, substituted pentacyclo[5.4.0.0 2,6.03,*0.05,9]undecanes (PCUs).z Understanding those factors that contribute to both stereoselectivity and regioselectivity in Diels-Alder reactions is important in determining how to use and control the reaction in organic synthesis. Our previous studies1s3 on the reaction of la with symmetrical dienophiles have demonstrated that n-facial selectivity can in general be predicted by molecular mechanics calculations. In an effort to determine if such calculations are also useful in predicting regioselectivity, we have undertaken a study of the Diels-Alder cycloadditions of unsymmetrical dienophiles to facially differentiated and unsymmetrically substituted hexacyclo[l0.2.1.0~~tt.~~~.~~t4.O~~t~]pentadecadienes lb-f. SYNTHESES OF DIELS-ALDER DIENES The starting material, la, can be prepared readily in large quantity in two synthetic steps by starting with cyclopentadiene and 1,4-naphthoquinone. 3bA Diene lc, mp 128-129 "C, was prepared in 90% yield by refluxing a benzene solution of la with excess ethylene glycol in the presence of a catalytic 13037 13038 J. M. COXON et al. amount of p-TsOH.3h Subsequent Wolff-Kishner reduction5 of lc afforded 1 b (36%. mp 53 "C). The yield of lb was increased to 56% by using the modified Wolff-Kishner reduction procedure developed by Paquette and coworkers.6 Hydrolysis of lb with aqueous oxalic acid produced Id quantitatively. Reduction of lc and of Id with ethanolic NaBa afforded If and le, respectively, both in essentially
Helvetica Chimica Acta, 1998
A correlation between the solvent polarity and the logarithm of the diastereoisomer ratio (dr) was found for the uncatalyzed [4 2] cycloaddition of cyclopentadiene to N,N'-fumaroyldi[(2R )-bornane-10,2-sultam]. Using the Abboud-Abraham-Kamlet-Taft parameters, predictive values for this method, allowed an optimum diastereoisomeric excess (de) of 96% ( EtOH, À 788). A similar diastereoselectivity was achieved using 5m LiClO 4 /Et 2 O or H 2 O/b-cyclodextrin, and the influence of supercritical CO 2 is also reported. Selective cycloadditions of apolar diene in polar solvents are entropically favored by the greater dipole moment of the Nenoylcamphorsultam syn-s-cis conformers and of the C(a)-re transition states. Implications on the stereochemical course of the reaction are discussed.
Organometallics, 2005
A study of reactivity and facial selectivity in Diels-Alder reactions of the Fischer carbene complexes (CO) 5 MdC(CtCC 6 H 4 R)OCH 2 CH 3 (1a, M ) Cr, R ) H; 1b, M ) Cr, R ) p-OCH 3 ; 1c, M ) Cr, R ) p-CH 3 ; 2, M ) W, R ) H; 3, M ) Mo, R ) H), with 1,2,3,4,5pentamethylcyclopenta-1,3-diene (4) was carried out. The cycloadditions were found to be highly π-facial stereoselective, favoring the anti adduct. Among these complexes, 3 was the most reactive dienophile. The stereochemical assignment of the adducts 5-7 was supported by NOE measurements; structures of the anti cycloadducts 5a and 6 were established by single-crystal X-ray diffraction. A [4 + 2] cycloaddition/benzannulation/rearrangement cascade reaction was observed for the chromium carbene complexes 1a-c with 4 under thermal conditions, resulting in the naphthofurandione derivatives 9-11. Recently, we reported the reactivity and selectivity in the reaction of (R-alkoxyvinyl)ethoxycarbene complexes with 1,2,3,4,5-pentamethyl-1,3-cyclopentadiene, which produced new alkoxy-chelated tetracarbonyl carbene complexes with a high anti/exo selectivity. 6 This study has now been extended to the reaction of the (arylethynyl)ethoxycarbene complexes 1-3 in Diels-Alder cycloadditions. Herein, we describe the cycloaddition of (arylethynyl)ethoxycarbene complexes 1-3 with 1,2,3,4,5-pentam- † Escuela Nacional de Ciencias Biológicas, IPN. ‡ Facultad de Estudios Superiores Cuautitlá n-UNAM. § Universidad Nacional Autónoma de México.
ChemistrySelect, 2017
Recently, we found that the Diels–Alder reaction between levoglucosenone and the acetonide of (1S,2R)‐3‐methylcyclohexa‐3,5‐diene‐1,2‐diol occurs through the most hindered face of the diene. This unexpected facial selectivity has no precedent for di‐O‐isopropylidene‐protected dienes, and the reasons behind it remain unclear. Here, we expand on our earlier findings, computationally assessing the structural and electronic factors responsible for this unforeseen stereoselectivity. The B3LYP/6‐31+G(d,p) results identify the three main adducts (β‐endo‐ortho:α‐endo‐meta:α‐exo‐ortho), giving a product ratio (63:9:28) that is in line with the experimental value (64:16:10). The β‐endo attack allows to maximize the electrostatic attraction between the reactants, giving rise to dipolar C−O⋅⋅⋅H−C interactions with the isopropylidene group at the transition state. The endo/exo preference can be rationalized through electrostatic repulsion and steric hindrance between the isopropylidene and methy...