Naphthoquinones, chiral, Diels-Alder reaction

A wide variety of chiral sulfinyl substituents have been employed as chiral auxiliaries on both dienes162 and dienophiles163 in asymmetric Diels-Alder reactions. Carreno and colleagues164, for example, used Diels-Alder reactions of (Ss)-2-(p-tolylsulfinyl)-1,4-naphthoquinone (249) to separate racemic mixtures of a wide variety of diene ena-tiomers 250a and 250b via kinetic resolution and to obtain enantiomerically enriched... 

Brimble and coworkers176 studied the asymmetric Diels-Alder reactions of cyclopentadiene with chiral naphthoquinones 272 bearing different chiral auxiliaries. The highest endo and facial selectivities were obtained using zinc dichloride as the Lewis acid catalyst and (—)-pantolactone as the chiral auxiliary. Thus, the reaction between cyclopentadiene and 272 afforded a 98 2 mixture of 273 and 274 (equation 76). The chiral auxiliary was removed easily by lithium borohydride reduction. 

Chiral bis(oxazoline)/Copper(II) complexes are evaluated for asymmetric Diels-Alder reaction of naphthoquinone derivatives, and moderate levels of enantiomeric excess are observed in certain cases [56] (Eq. 8A.33). 

Diels-Alder Reaction. The Diels-Alder reaction of methacrolein with 1,3-dienol derivatives can also be catalyzed by the chiral BINOL-derived titanium complex BINOL-T1CI2. The endo adduct was obtained in high enantioselectivity (eq 15). The sense of asymmetric induction is exactly the same as observed for the asymmetric catalytic reactions shown above. Asymmetric catalytic Diels-Alder reactions with naphthoquinone derivatives as a dienophile provide an efficient entry to the asymmetric synthesis of anthracyclinone aglycones (eq 16). ... 

Silica gel has been reported to accelerate Diels-Alder reactions of 3-methoxy-carbonyl-2-pyrone and a related chiral dienophile with butyl vinyl ether or benzyl vinyl ether (Scheme 4) [31]. Related dienophiles, 4,6-disubstituted 2-pyrones, were investigated in reactions with naphthoquinone or A-phenylmaleimide catalyzed by silica or other heterogeneous catalysts in the absence of solvent [32], An example is included in Scheme 4. 

The alkoxy dienes (6) containing a chiral carbohydrate auxiliary each undergo a highly stereoselective Diels-Alder reaction with naphthoquinone affording adducts (7). The vinyl ether (8), on treatment with tosyl isocyanate, stereoselectively produced the -lactam derivative (9). ... 

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