Diels cyclopentadiene with 3-acryloyl

Ghosh found that the cationic () )-BINAP-Pd(II) complex efficiently catalyzed the asymmetric Diels-Alder reaction of cyclopentadiene with acryloyl-A -oxazolidinone (31) at —78" C, and obtained the en[Pg.618]

In 2000, Nakano et al. developed N-P type ligand, chiral phosphinooxazoline (POZ) (59) and found that the Pd complexes (61a-c) of ligand (59) works as an effective catalyst of asymmetric ally lie alkylation (Schemes 16.17 and 16.18) [19]. Recently, they have reported that cationic Pd- and Pt-POZ (59) catalysts are effective in Diels-Alder reactions on various substrates. The cationic Pd-POZ (59) complex (61c) provided particularly excellent enantioselectivity up to 98% ee in the Diels-Alder reactions of cyclopentadiene with acryloyl (15a), crotonoyl (15b), and fumaroyl-oxazolidinones (15c) (Scheme 16.18). The Pd and Pt complexes with POZ ligands that they explored have a characteristic structure therefore, they should prove useful not only for other Diels-Alder reactions but also for other asymmetric processes. 

Bolm et al. [106] have carefully studied the synthesis and the hganding ability of salen-like bis(sulfoximines). The chirahty which is indeed generally introduced via the use of chiral diamines in the salen series, is in sulfoximines present via the sulfur atom. They investigated the Diels-Alder cycloaddition between cyclopentadiene and acryloyl-2-oxazolidinones with various bis(sulfoximines) (see Scheme 42) and Cu(OTf)2 as the copper source [107]. 

In 2005, Carretero et al. reported a second example of chiral catalysts based on S/P-coordination employed in the catalysis of the enantioselective Diels-Alder reaction, namely palladium complexes of chiral planar l-phosphino-2-sulfenylferrocenes (Fesulphos). This new family of chiral ligands afforded, in the presence of PdCl2, high enantioselectivities of up to 95% ee, in the asymmetric Diels-Alder reaction of cyclopentadiene with A-acryloyl-l,3-oxazolidin-2-one (Scheme 5.17). The S/P-bidentate character of the Fesulphos ligands has been proved by X-ray diffraction analysis of several metal complexes. When the reaction was performed in the presence of the corresponding copper-chelates, a lower and opposite enantioselectivity was obtained. This difference of results was explained by the geometry of the palladium (square-planar) and copper (tetrahedral) complexes. 

Diels-Alder Cycloadditions (AUcene -+ Six-Membered Cycloadduct). lV-Acryloyl-a-methyltoluene-2,a-sultam (3a) participates in highly endo and C(a)-re ir-face selective Lewis acid promoted Diels-Alder reactions with Cyclopentadiene, 1,3-Butadiene, and Isoprene (eq 2 and Table 1). These levels of induction compare favorably with most alternative auxiliaries, including the 10,2-camphorsultam. However, V-crotonyl-a-methyltoluene-2,a-sultam (ent-3b) reacts with cyclopentadiene with only mod-... 

The effect of the ligand bite angle on the enantioselectivity in the copper(n) catalyzed Diels-Alder reaction of cyclopentadiene with A-acryloyl-l,3-oxazoUdin-2-one was studied using spiro bis(oxazolidine) based complexes 431a-d (Table The data... 

A third approach to brefeldin A by Greene dealt with a version of the second synthesis designed to provide optically active 161, as shown in Scheme 1.39. Enantiomerically pure alcohol (S)-( -i- )-240, obtained via resolution of the derived phthalate mono ester with brucine, was acylated with acryloyl chloride to afford 241. Lewis acid promoted Diels-Alder reaction of 241 and cyclopentadiene then led to a 75% yield of diastereomers 242a (endo) and 242b (exo) in a 97 3 ratio. 

Diels-Alder reactions of cyclopentadiene with methyl acrylate [19], (-)-menthyl acrylate, or other chiral dienophiles [20-23] catalyzed by cation-exchanged KIO montmorillonites were thoroughly investigated by Mayoral and co-workers. The structures of the chiral dienophiles are depicted in Figure 1. Moderate diastereo-selectivities were obtained with (-)-menthyl acrylate (54 %) and (7 )-f -acryloyl-pantolactone (53 %) in reactions catalyzed by zinc(II)-exchanged KIO montmoril-lonite at —20 °C. 

A diastereoselective Diels-Alder reaction of cyclopentadiene with a chiral dienophile, iV,iV -fumaroyldi[(2/ )-bornane-10,2-sultam], was carried out in scC02. The highest diastereoselectivity (65% conversion and 93% de) is obtained around the critical point (74 bar) at 33 C. Lanthanide triflate catalyzes the reaction of cyclopentadiene and 3-acryloyl-(4S)-isopropyloxazolidin-2-one 21 in SCCO2 to give the endo adduct endo exo = 10 30) with a higher diastereoselectivity (59% de) than in CH2CI2 (38-42% de) (Scheme 36). ... 

A comparative study on the influence of different lanthanide cations and the substituents at the 4 and 5 -positions in the pybox ligands in the Diels-Alder reaction of cyclopentadiene with 3-acryloyl-l,3-oxazolidin-2-one was realized [135], Of the catalysts derived from (4 P,5 P)-4-Me-5-Ph-pybox, the Sc(III)-based one is both strongly endo selective (endo/exo = 97/3) and highly enantioselective (97% ee (endo)). Later, it was found that the scandium-(4 S,5 S)-4-CH20TIPS-5-Ph-pybox complex also gave endo selective (endo/exo = 92/8-96/4) and highly enantioselective (93-99% ee (endo)) for the Diels-Alder reactions of cyclopentadiene with 3-acryloyl-or 3-crotonoyloxazolidinones. 

The best result was obtained from the o-tolyl substitution of phosphorus. The palladium catalysts derived from (62) afforded high enantioselectivities up to 95% ee in the Diels-Alder reaction of cyclopentadiene with N-acryloyl-oxazolidinone (15a). In addition, a similar result was obtained from the dibromo complex (PdBr2) and AgOTf as halogen scavenger provided 90% of enantioselectivity. 

Norbornene-2-carboxylic acid (8) was obtained in acceptable ee by the use of a chiral auxiliary. Optically active tetrahydropyrimidones 6 underwent Diels-Alder cycloadditions with cyclopentadiene (5) in water at room temperature. Subsequent removal of the auxiliary was achieved by boiling the carboxamide 7 in water (Scheme 5.2). The cycloaddition conversions were at least 90% and the endo adduct was the prevalent diastereoisomer. Using 70% aqueous ethanol as reaction medium, both the endo/exo ratio and ee were lower than in pure water. Since tetrahydropyrimidones 6 can be prepared in water from L-asparagine and a suitable aldehyde and subsequent acylation with acryloyl chloride, the entire synthesis of 8 was performed in water by one-pot procedure. The yield was fair, but the ee of norbornene carboxylic acid 8 was lower than that obtained by using a step-by-step procedure. This result was probably due to some acryloyl chloride being hydrolyzed to acrylic acid, which then reacted with 5 in a non-stereo-biased manner. 

A quinoline-phosphine ligand has been developed by Buono et ah, and its complex 29 with Cu(OTf)2 found to be an effective catalyst for the Diels-Alder reaction between acryloyl-oxazolidinone and cyclopentadiene, affording the cycloadduct... 

This procedure describes the preparation and application of an effective chiral catalyst for the enantioselective Diels-Alder reaction.11 The catalyst is derived from optically active 1,2-diphenylethylenediamine, the preparation of which (either antipode) was described in the preceding procedure. The aluminum-based Lewis acid also catalyzes the cycloaddition of crotonoyl oxazolidinones with cyclopentadiene,11 and acryloyl derivatives with benzyloxymethylene-cyclopentadiene. The latter reaction leads to optically pure intermediates for synthesis of prostaglandins.11... 

Narasaka et al.16 reported that 53 catalyzes Diels-Alder reactions of 54-type substrates with diene in the presence of 4 A molecular sieves (Scheme 5-18). A remarkable solvent effect on the enantioselectivity is observed. High enantio-selectivity is attained using mesitylene as the solvent. As shown in Scheme 5-18, the reaction of 54a with isoprene proceeds smoothly in this solvent, affording product 55a with 92% ee. Other 3-(3-substituted acryloyl)-l,3-oxazolidin-2-ones 54b-d also give good results (75-91% ee) when reacted with cyclopentadiene. 

Sudo and Saigo153 reported the application of ds-2-amino-3,3-dimethyl-l-indanol derived l,3-oxazolidin-2-one 231 as a chiral auxiliary in asymmetric Diels-Alder reactions. The TV-crotonyl and TV-acryloyl derivatives were reacted with cyclopentadiene, 1,3-cyclohexadiene, isoprene and 2,3-dimethyl-l,3-butadiene, using diethylaluminum chloride as the Lewis acid catalyst. The reactions afforded the expected cycloadducts in moderate to high yields (33-97%) with high endo selectivities and high de values (92% to >98%). 

Kunieda and colleagues155 used a similar kind of l,3-oxazolidin-2-one (234) and studied the diethylaluminum chloride and boron trifluoride etherate catalyzed Diels-Alder reactions of its A-acryloyl and A-crotonyl derivatives with cyclopentadiene. The yields were high (80-100%), the reactions being almost completely endo selective. The diastere-omeric excesses obtained ranged from 71% to more than 99%. 

Oppolzer and colleagues performed pioneering work on the application of chiral sultam based dienophiles in asymmetric Diels-Alder reactions. The bomanesultam based dienophiles provided excellent de values in the Lewis acid mediated Diels-Alder reactions with a wide variety of dienes179. The efficiency of the simpler toluene-2,a-sultam based dienophiles was also studied180. Chiral auxiliary 282 proved superior to 283 and 284 in the aluminum Lewis acid catalyzed Diels-Alder reactions of its A-acryloyl derivative with cyclopentadiene, 1,3-butadiene and isoprene, affording the adducts with >90% de. 

Since high enantioselectivity was achieved by employing two molar equivalents of the chiral titanium reagent generated from 17b, the asymmetric Diels-Alder reaction of various oxazolidone derivatives of a,8-unsaturated acids and cyclopentadiene was studied. The results are listed in Table 4. With the exception of the acryloyl derivative 15b, various dienophiles reacted with cyclopentadiene to give the endo-adducts 1 in high optical purity. 

Metal complexes of bis(oxazoline) ligands are excellent catalysts for the enantioselective Diels-Alder reaction of cyclopentadiene and 3-acryloyl-l,3-oxa-zolidin-2-one. This reaction was most commonly utilized for initial investigation of the catalytic system. The selectivity in this reaction can be twofold. Approach of the dienophile (in this case, 3-acryloyl-l,3-oxazolidin-2-one) can be from the endo or exo face and the orientation of the oxazolidinone ring can lead to formation of either enantiomer R or S) on each face. The ideal catalyst would offer control over both of these factors leading to reaction at exclusively one face (endo or exo) and yielding exclusively one enantiomer. Corey and co-workers first experimented with the use of bis(oxazoline)-metal complexes as catalysts in the Diels-Alder reaction between cyclopentadiene 68 and 3-acryloyl-l,3-oxazolidin-2-one 69 the results are summarized in Table 9.7 (Fig. 9.20). For this reaction, 10 mol% of various iron(III)-phe-box 6 complexes were utilized at a reaction temperature of —50 °C for 2-15 h. The yields of cycloadducts were 85%. The best selectivities were observed when iron(III) chloride was used as the metal source and the reaction was stirred at —50 °C for 15 h. Under these conditions the facial selectivity was determined to be 99 1 (endo/exo) with an endo ee of 84%. 

In 1993, Evans and co-workers examined phe-box 6, /-pr-box 45, and bu-box 3 ligands in the Diels-Alder reaction of cyclopentadiene 68 and 3-acryloyl-l,3-oxazolidin-2-one 69 using a weak Lewis acid such as copper(II) triflate." The results are summarized in Table 9.9. The reaction was carried out between —50 and —78 °C for 3-18 h and achieved selectivities of up to 98 2 (endo/exo) with an endo ee of >98% (using bu-box 3). Interestingly, the enantiomer produced in these reactions was the (25) configuration, compared to the (2K) isomer obtained with iron(III) and magnesium(II) as reported by Corey. This observed stereochemistry was explained by the chelation model of the copper(II) complex 74 (Fig. 9.23)... 

Diels-Alder reactions involving bis(oxazoline) ligands are not limited to the reaction between cyclopentadiene and 3-acryloyl-l,3,-oxazolidin-2-one they can be used with a wide variety of dienes and dienophiles. Evans demonstrated the utility of py-box ligand Id in the reaction between cyclopentadiene 68 and various... 

Diels-Alder reactions of (Z)-A -substituted-4-methylene-5-propylidene-2-oxazoli-dinone dienes with methyl vinyl ketone, methyl propiolate, and captodative alkenes yield the highest regio- and stereo-selectivities in mixtures of H20 and MeOH or under BF3.Et20 catalysis.198 The asymmetric Diels-Alder reaction of cyclopentadiene and 3-acryloyl-2-oxazolidinone is catalysed by a new Cu(II) catalyst containing a chiral sterically congested roofed (2-diphenylphosphino)phenylthiazoline ligand (169).199... 

Enantioselective Diels-Alder reaction. Highly stereoselective Diels-Alder reactions can be achieved by use of the 4,4 -diphenylbis(oxazoline) 2b, prepared from (+)-phenylglycinol, as a chiral, bidentate ligand for iron salts. Thus reaction of Fel3 with 2b and I2 in CH3CN forms a complex presumed to be I-Fel3, which can catalyze reaction of 3-acryloyl-l,3-oxazolidin-2-one with cyclopentadiene at —50° to give the endo-adduct in 95% yield. The product is the 2R-enantiomer (82% ee). 

Acryloyl and crotonoyl amides (9) derived from the sultam (8), available from ( + )-l, are somewhat more reactive dienophiles than the i orresponding esters (3) derived from 2. Diels-Alder reactions of 9 with cyclopentadiene catalyzed by TiCU or C2H,AIC1, proceed in high yield, with high endo selectivity ( 99%) ind diastereoselectivity of —95% de. The chiral auxiliary is removed by reduction witfi LiAIH4 to furnish 8 and the chiral alcohol in 89-95% yield.-... 

These catalyst precursors, abbreviated N2PdCl2 in equation (7), were then employed in the asymmetric Diels Alder reaction of A-acryloyl oxazolidinone with cyclopentadiene (equation 8). 

Thermal reactions of Al-enoylsultams generally show only moderate endo and r-face selectivity, e.g. Al-acryloyl- and N-crotonoyl-10,2-camphorsultams (4) and (6) with cyclopentadiene (eq 3, Table 1). The thermal hetero-Diels-Alder reaction of Al-glyoxaloyl-10,2-camphorsultam with 1-methoxybuta-... 

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