Hetero-Diels—Alder reactions of Danishefsky’s diene

Bis(trifluoromethanesulfonylamides) ligand was also used by Mikami et al., in 1995, for the lanthanide-catalysed hetero-Diels-Alder reaction of Danishefsky s diene with butyl glyoxylate. This reaction produced the corresponding... 

Schaus et al.41 have also reported an asymmetric hetero Diels-Alder reaction of Danishefsky s diene 10042 with aldehyde 101 catalyzed by chromium(III) complex 99 bearing a similar chiral salen ligand. Product 102 is obtained in moderate to good yield and stereoselectivity (Scheme 5-31 and Table 5-5). 

TADDOL-Promoted Enantioselective Hetero-Diels-Alder Reaction of Danishefsky s Diene 37... 

Inda-box ent-9a has been used recently in the production of the natural product (-)-malyngolide 265. " The key step of the synthesis by Ghosh and Shirai, as shown in Figure 9.80, is the hetero-Diels-Alder reaction of Danishefsky s diene 112 and cx-ketoester 263 to afford the pyranone derivative 264 in 77% yield and 47% ee that was converted into (—)-malyngolide in several additional steps. The preparation of different pyranones was investigated using different ot-ketoesters. 

TABLE 9.18 HETERO DIELS-ALDER REACTION OF DANISHEFSKY S DIENE WITH GLYOXYLATE ESTERS, 558... 

A similar chiral bis(oxazoline)/Cu(II) catalyst is useful for the asymmetric hetero Diels-Alder reaction of Danishefsky s diene and glyoxylates [63] (Eq. 8A.39). Other bis(oxa-zoline)/M(OTf)2 (M = Sn, Mg) complexes are not effective. This method provides new routes to asymmetric aldol synthesis upon hydrolysis of the resulting adducts. 

Jacobsen studied the efficiency of a series of chiral (salen)Cr(III)X complex (X = Cl, N 3, F, BF4) for the asymmetric hetero Diels-Alder reaction of Danishefsky s diene with aldehydes. The best result was obtained with the terafluoroborate catalyst [65] (Eq. 8A.41). 

A series of trivalent lanthanoid complexes, scandium, and ytterbium tris-(R)-(-)-1,1 -binaphthyl-2,2 -diyl phosphonate, have been introduced as new chiral and stable Lewis acids for the asymmetric hetero Diels-Alder reaction of Danishefsky s diene and aldehydes. 2,6-Lutidine was found to be an effective additive to improve the enantioselectivity up to 89% ee [66] (Eq. 8A.42). 

Motoyama, Y., Koga, Y., Nishiyama, H. Asymmetric hetero Diels-Alder reaction of Danishefsky s dienes and glyoxylates with chiral bis(oxazolinyl)phenylrhodium(lll) aqua complexes, and its mechanistic studies. Tetrahedron 2001, 57, 853-860. 

Keck, G. E., Li, X.-Y., Krishnamurthy, D. Catalytic Enantioselective Synthesis of Dihydropyrones via Formal Hetero Diels-Alder Reactions of "Danishefsky s Diene" with Aldehydes. J. Org. Chem. 1995, 60, 5998-5999. 

Mikami and coworkers also reported the development of lanthanide bis(trif-luoromethanesulfonyl)amides (bistrifylamides) as a new type of asymmetric catalysts for the hetero-Diels-Alder reaction of Danishefsky s diene, wherein the significant effect of water as an additive is observed in increasing not only the enan-tioselectivity but also the chemical yield. Bistrifylamides can be used as effective bidentate Hgands to increase the Lewis acidity of their chiral metal complexes on account of the higher acidity of the conjugated acids than those of afiphatic and aromatic diols, which are commonly used as chiral bidentate hgands [33]. 

Aryl-2,3-dihydro-4-pyranones. The hetero-Diels-Alder reaction of Danishefsky s diene and aromatic aldehydes is catalyzed by the metallocenium complex. The adducts are readily hydrolyzed. 

Scheme 3,37 Hetero-Diels-Alder reaction of Danishefsky s diene with benzaldehyde...

Tridentate bis(oxazolinyl)pyridinyl rhodium and ruthenium pincer complexes are useful as catalysts for hydrosilylations and cyclopropanations. These NNN-type inorganic pincer complexes are not as stable, however, as phosphine or salen-type pincer complexes. On the other hand, an organometallic tridentate bis(oxazolinyl) phenyl NCN-type complex is stable. These optically active NCN-type pincer complexes act as efficient catalysts for enantioselective hetero Diels-Alder reactions of Danishefsky s diene with glyoxylates [26]. 

In the asymmetric hetero Diels-Alder reactions of Danishefsky s diene by chiral lanthanide bis(trifluoromethane-sulfonyl)amide (bis-triflamide) complexes, particularly 5rttrimn bis-triflamide, a significant effect of water as an additive was observed in increasing not only the enantioselectivity but also the chemical yields (Scheme 28). ... 

Hetero Diels-Alder reaction of Danishefsky s diene with imines is a powerful method for the preparation of dihydropyridone derivatives. HBF4 also catalyzed this reaction using aromatic and aliphatic imines that were prepared in situ from the corresponding aromatic or aliphatic aldehydes and aromatic amines (Scheme 3.5). 

The hetero Diels-Alder reaction of Danishefsky s diene (26) with benzaldehyde was explored using catalysis by various chiral rare earth salts (Scheme 16) [33]. It was found that this reaction gave better yields of 27 in supercritic CO2, but without significant improvement of the enantioselectivity with respect to the conventional method. 

Asymmetric hetero-Diels-Alder reaction of Danishefsky s diene with glyoxylate is efficiently catalyzed by the phebox-Rh(III) complexes 1 [12]. With 2 mol% of the benzyl phebox-Rh complex 1-Bn, the reaction tookplace at —78°C for 1 h to give the corresponding dihydropyran derivatives 10 in high yields with good ee s (Scheme 4). 

A chiral bis-sulfonamide catalyst (35) was developed by Tonoi and Mikami and glyoxylates underwent hetero Diels-Alder reaction of Danishefsky s diene to give cyclohexenone derivatives with high ees (Scheme 2.78) [146]. 

The increased Lewis acidity of (165) was tested in the hetero Diels-Alder reaction of Danishefsky s diene (168) with benzaldehyde to obtain the dihydropyranone... 

The enantioselective hetero-Diels-Alder reaction of siloxydienes, such as Danishefsky s and Brassard s dienes, with imines provides an efficient route for the preparation of functionalized nitrogen-containing heterocycles in optically active forms. Akiyama and coworkers reported the first catalytic enantioselective hetero-Diels-Alder reaction of Danishefsky s diene (21) with aromatic imines 20 using chiral phosphoric acid catalyst la (Scheme 11.7a) [14]. The desired dihydropyridi-nones 22 were obtained in good yields with high enantioselectivities. Notably, the addition of an equimolar amount of acetic acid was effective in improving the enantioselectivity. Akiyama and coworkers also reported an enantioselective... 

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