Menthyl acrylate

Clay-catalyzed asymmetric Diels-Alder reactions were investigated by using chiral acrylates [10]. Zn(II)- and Ti(IV)-K-10 montmorillonite, calcined at 55 °C, did not efficiently catalyze the cycloadditions of cyclopentadiene (1) with acrylates that incorporate large-size chiral auxiliaries such as cA-3-neopentoxyisobornyl acrylate (2) and (-)-menthyl acrylate (3, R = H) (Figure 4.1). This result was probably due to diffusion problems. 

Gholami and Talebi have recently demonstrated that the GIPF technique can be utilized in analyzing the effects of solvents upon chemical reactions.61 They focused upon the Diels-Alder reaction between cyclopentadiene and menthyl acrylate in 15 different... 

More recently, such studies have been extended to nonhydrocarbon chiral comonomers, for example, menthyl acrylate and menthyl methacrylate (379, 382). Of notable interest, especially for microsequence investigation, are fluorescence studies combined with CD spectra carried out on copolymers containing the caibazole fragment (382). It is interesting to note that the induction of... 

The most widely investigated optically active poly-acrylic-esters are the polymers of bomyl and menthyl acrylate and methacrylate in this case the monomers have been polymerized by radical polymerization using benzoyl-peroxide (135), A. I. B. N. (134, 135), y-rays (131, 135), U. V. rays (4) in the presence of benzoin (134), and by anionic polymerization using LiC4H9 (4, 135) or C6H5MgBr (134, 135) as catalyst. 

Poly-[(lR,3R,4S)-l-rriethyl-4-isopropyl-cyclohex-3-yl]-acrylate Poly- —) -menthyl-acrylate 1 o o, o, 3 3 3 (131) ... 

In fact Schulz and co-workers (131,134), and Klabunovskii, Shvartsman and Petrov (55) report that the O. R. D. curves of poly-menthyl-acrylate, poly-bornyl-acrylate and poly-2-methyl-butyl-methacrylate show a maximum at about 300 mp, the wavelength corresponding to the maximum being related to the method of preparation of the polymer. Circular dichroism measurements seem advisable in order to confirm the existence of a Cotton effect postulated by the above authors in that wavelength range. 

Kotsuki et al.909 have developed a method to effect the Michael addition of [3-ketoesters with ethyl acrylate in the presence of triflic acid under solvent-free conditions [Eq. (5.335)]. Nonactivated cyclohexanones as Michael donors and a,/3-unsaturated ketones as acceptors are also reactive. The use of menthyl acrylates did not result in any significant asymmetric induction. 

Asymmetric Diels-Alder reactions. The acrylate of (+ )-l is markedly superior to ( —)-menthyl acrylate in effecting asymmetric induction in Diels-Alder reaction with cyclopentadiene (Lewis acid catalysis, equation I). A chiral intermediate in Corey s prostaglandin synthesis was obtained by the reaction of (-1- )-8-phenylmenthyl acrylate with a cyclopentadiene derivative.1... 

During the course of the Baylis-Hillman-reaction two stereocenters are formed, one of which remains in the Baylis-Hillman-product. An obvious concept for the development of an asymmetric version of the reaction represents the use of an enantiomerically pure acrylic acid derivative. The use of enantiomerically pure menthyl acrylates resulted, but only in certain cases, to respectable diastereomeric excesses [21]. A significant improvement was reported in 1997 by Leahy and coworkers who used the Oppolzer-sultame as a chiral auxiliary in DABCO-catalyzed Baylis-Hillman-reactions (Scheme 2) [22]. In this reaction, the... 

The rate and yield of the cycloaddition of 43a to menthyl acrylate 44 in toluene were found to be directly related to the basicity of the base used. Thus, yield and rate... 

Since Barton decarboxylation can be performed under mild conditions, thermal or photolytic treatment of the Barton ester (13) of propionic acid with TV-hydroxy-2-thiopyridone in the presence of chiral menthyl acrylates generates addition products (14). However, diastereoselectivity is rather poor, since the chiral menthyl center is too far away from the C-C bond-forming position, as shown in eq. 10.7. When the chiral center is adjacent to the reaction position, stereocontrol is significantly affected, as shown in eq. 10.8 [9-12]. 

Proline and isatin also furnish an azomethine ylide, which reacts regio- and stereo-selectively with acrylates, such as (1R, 2S, 5R)-menthyl acrylate, to yield a mixture of diastereoisomers. The structure of the major diastereoisomer was determined by X-ray crystallography and the following transition state was proposed for its formation286 (Scheme 66) ... 

Phenylmenthyl acrylate has been used as a component in an asymmetric Baylis-Hillman reaction. Treatment of the acrylate with 1,4-Diazabicyclo[2.2.2]octane and benzaldehyde at 8 kbar of pressure delivers the a-(hydroxyalkyl)acrylate (eq 8). The product obtained has an 86% de. Menthyl acrylate is superior to the phenylmenthyl acrylate in this particular application. In a radical-mediated addition, phenylmenthyl acrylate gives rise to the a-pyridyl sulfide in 68% yield (eq 9). The final product is isolated with a 56% de. 

In order to investigate in more detail the relationships between structure and photoinitiation activity in the polymeric systems based on benzoin methyl ether moieties, poly(MBA) and copolymers of MBA with menthyl acrylate [poly(MBA-co-MtA)s] have also been checked as photoinitiators and compared with the homopolymer of ot-vinyloxymethylbenzoin methyl ether and its copolymers with menthyl vinyl ether [poly(MBVE) and poly(MBVE-co-MtVE)s, respectively] [61,84]. 

The diastereomeric excess increases steadily as the activity of the alumina increases, i. e. when its Lewis character increases. Results obtained for menthyl acrylate cycloaddition with cyclopentadiene were rather similar but not as important [36] endolexo increase from 2.4 to 8.1 changing non-activated alumina for a pre-heated one at 200°C). 

Cydoadditions of dienes with menthyl acrylates are usually poorly selective unless the cooperative effect ( 1.6) is used with diesters. As early as 1963, Wal-borsky and coworkers observed an interesting selectivity in TiCl4 catalyzed reaction of 1,3-butadiene with dimenthyl fumarate 1.22. This reaction has been generalized by Yamamoto and coworkers, who performed it at low temperature (-78° to -40°C) in the presence of Et2AlCl (Figure 9.23). 

The (/ )-menthyl acrylate 28c produces in the [4 + 2] cycloaddition with cyclopentadiene (2) the endo-adduct 33 and the e.vo-adduct 34 as major components with very low selectivity5. Cycloadditions to 1,3-butadiene (6a), 2,3-dimethyl-l,3-butadiene (6c) and 1,3-cyclohexadiene (3) also give the corresponding adducts with a low diastereoselectivity, even under high pressure6. 

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. 

K10 montmorillonites exchanged with different cations, dried at 120°C or calcined at 550°C, are used as catalysts in Diels-Alder reactions of methyl and (-)-menthyl acrylates with cyclopentadiene. In general, calcined clays give rise to better conversions and selectivities. Zr(IV) and specially Ti(IV) clays display the best catalytic activities. However, the best asymmetric induction is achieved with Cr(lll) and Ca(ll) calcined clays. Clays containing easily reducible cations behave differently due to the cyclopentadiene polymerization via radical cations. 

Clays [2] and zeolites [3] have been reported as good catalysts for Diels-Alder synthesis. Recently, we have studied the Diels-Alder cycloaddition between methyl acrylate (1) and cyclopentadiene (2) (Figure 1) and have shown that the solvent [4], the calcination of the solid [5] and the exchanged cation [6] play a decisive role. We now report the results obtained from the reactions of cyclopentadiene with methyl and (-)-menthyl acrylates, catalysed by K10 montmorillonites exchanged with different cations and dried at 120°C or calcined at 550°C. 

The heterogeneous catalysis of the benchmark asymmetric Diels-Alder reaction between (-)-menthyl acrylate (4) and cyclopentadiene (2) (Figure 2) with both dried [12] and calcined [5] Zn(ll)-clays has shown that selectivities close to... 

The results obtained from the reaction were determined by gas chromatography, (5a) and (5b) were assigned by a comparison of the gas chromatograms obtained in several clay-catalysed reactions with those obtained in several reactions of (-)-menthyl acrylate with cyclopentadiene using homogeneous catalysts, whose diastereoselectivities and absolute configurations have been described [11]. 

Chiral induction in cycloaddition reactions of azomethine ylide has been achieved when the a-amino acid (233) reacts with isatin or benzthiophen derivatives (234 X = NH, NBu, S) and menthyl acrylate. The course of the reactions involves decarboxylative azomethine ylide formation followed by cycloaddition through an endo transition state ultimately affording the cycloadduct (61) (Table 9) in 67-82% diastereomeric excess <91TL5417>. 

Table 11.13. Selectivity in the Diels-Alder Reaction of Cyclopentadiene and Menthyl Acrylate...

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