Heteroatom Diels-Alder,

Catalysts such as Fe(BuEtCHC02)3 have been d eloped that are effective for the heteroatom Diels-Alder reaction. Indium trichloride (InCls) is a good catalyst for imino-Diels-Alder reactions. Hetero-Diels-Alder reactions involving carbonyls have been done in water. Ultrasound has been used to promote the Diels-Alder reactions of 1-azadienes. ... 

Heteroatom Diels-Alder reactions that proceed with good to excellent asymmetric induction are well known. Chiral 1-aza-dienes have been developed as substrates, for example. ... 

Heteroatom Diels-Alder reaction of ketones and aldhydes... 

Table 4 Use of a electrophilic scavenger resin to improve yields in the heteroatom Diels-Alder reaction (Equation 34)...

The first report of a chiral aluminum Lewis acid employed in a heteroatom Diels-Alder reaction utilized Koga s mentholoxy dichloroaluminum catalyst 4 [75]. trans-Piperylene and 1-methoxybutadiene were reacted with n-butyl glyoxalate and diethyl mesoxalate the results are summarized in Sch. 46. The asymmetric induction and chemical yield in these reactions are quite poor but the authors did find that moderate asymmetric induction could be obtained from reactions catalyzed by Eu(hfc)3. 

The 3,3 -bis-triarylsilyl BINOL ligands 98 were first introduced by Maruoka, Itoh, Shirasaka, and Yamamoto for the heteroatom Diels-Alder reaction of electron-rich dienes with unactivated aldehydes [76,77], The catalyst was prepared by treating the BINOL 97 with trimethylaluminum in dichloromethane at room temperature for 1.5 h. The catalyst is pink to wine red and was found, by freezing point depression, to be a monomer. A typical procedure for the Diels-Alder reaction is illustrated for the reaction of the trisubstituted diene 371 and cyclohexylcarboxaldehyde. The reaction is complete with 10 mol % catalyst at -20 °C in 2 h in toluene and, after treatment with TFA to effect elimination of the methoxyl group, the product of the reaction is predominately the cii-pyrone 373. The triphenylsilyl substituted catalyst gives the product in 93 % ee (Sch. 47). 

Table 18. Asymmetric catalytic heteroatom Diels-Alder reactions of alkoxydienes.

Table 5) [28], and heteroatom Diels-Alder reactions (Sch. 50) [79,80] but no X-ray structure had ever been reported for it or for the 3,3 -disubstituted derivatives which were first introduced as an asymmetric Claisen catalyst [24-27]. Although compound 435 was found not to induce any reaction between cyclohexenone and phosphonate 425 under the standard conditions for catalyst 428, consistent with the proposed equilibrium of species 394, 431, 432, 433, and 434 is the finding that catalysis of the reactions between cyclohexenone or cyclopentenone and phosphonate 425 with a 2 1 mixture of 434 (M = Li) and 435 gave only the Michael adducts 426 and 427 in 96 % ee and 92 % ee, respectively. Because 394 and 432 are inactive catalysts and 434 results in much lower induction and some 1,2-adduct, it was proposed that the active catalyst in the Michael addition of phosphonate 425 to cyclohexenone was the species 431 resulting from association of ALB catalyst with a metal alkoxide. It was proposed that the stereochemical determining step involved intramolecular transfer of the enolate of 425 to the coordinated cyclohexenone in species 436. 

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