Dihydronaphthalene chromium complex

Diels-Alder reaction with cyclopentadiene gave the corresponding adduct (Eq. 31) [28]. (Dihydronaphthalene)chromium complex gave addition product by reaction with diazomethane with high diastereoselectivity [29]. The acrylate having chiral arene chromium complex underwent Diels-Alder reaction with high selectivity in the presence of Lewis acid (Eq. 32) [30]. 

When the trifluoromethyl group is the only electron-withdrawing. substituent of the cyclic dienophilc, such as in 4-(trifluoromethyl)-1,2-dihydronaphthalene, high pressure is required for the reaction to occur. The yield is improved when the reaction is performed with the tricarbonyl chromium complex 21 of 4-(trifluoromethyl)-l,2-dihydronaphthalene. In the reaction with l-methoxy-.3-(trimethylsiloxy)buta-l,3-diene (Danishefsky s diene, 4), the cycloadducts are obtained as a 1 1 mixture ofcHr/o/c.vo-addition products. They are easily converted into the (trifluoroniethyl)phenanthrenone 22 by the action of bromotrimethylsilane. 

The addition-protonation procedure maintains the arene-chromium bond and allows further application of the activating effect of the metal. In an approach to the synthesis of anthraquinone antibiotics, the dihydronaphthalene complex (79) was allowed to react with a cyanohydrin acetal anion and then quenched with acid.129 The resulting tetralin complex (80) could be metallated effectively and carried on to a key intermediate (81) in anthraquinone construction (equation 54)... 

Complexation of dihydronaphthalene with chromium tricarbonyl facilitates the attack of a nucleophilic amine and stereoselectively directs the protonation "anti" to the metal atom. (+)-(l S,2 R)-, 2-Dihydro-7-methoxy-1,4-dimethyl-1 - 2 -[methyl(trifiuoroacetyl)amino]propyl -naphthalene [(+)-7] was treated with chromium hexacarbonyl to give a mixture of a- and /(-chromium tricarbonyl complexes in a 10 1 ratio ( H NMR). The complexes were separated and the a-isomer cyclized by base treatment and sonication. Dccomplexation gave the ben-zomorphan tricycle 8 in low yield [40%, based on recovered (+)-7]18. The trifluoroacetyl protection of the amino group was necessary to achieve both stereoselective complexation with chromium tricarbonyl and successful cyclization. 

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