Alder reaction anisole

In the Mukaiyama aldol additions of trimethyl-(l-phenyl-propenyloxy)-silane to give benzaldehyde and cinnamaldehyde catalyzed by 7 mol% supported scandium catalyst, a 1 1 mixture of diastereomers was obtained. Again, the dendritic catalyst could be recycled easily without any loss in performance. The scandium cross-linked dendritic material appeared to be an efficient catalyst for the Diels-Alder reaction between methyl vinyl ketone and cyclopentadiene. The Diels-Alder adduct was formed in dichloromethane at 0°C in 79% yield with an endo/exo ratio of 85 15. The material was also used as a Friedel-Crafts acylation catalyst (contain-ing7mol% scandium) for the formation of / -methoxyacetophenone (in a 73% yield) from anisole, acetic acid anhydride, and lithium perchlorate at 50°C in nitromethane. 

For the synthesis of carazostatin (247), the required arylamine 708 was synthesized starting from 1-methoxycyclohexa-l, 3-diene (710) and methyl 2-decynoate (711). The key step in this route is the Diels-Alder cycloaddition of 710 and 711, followed by retro-Diels-Alder reaction with extrusion of ethylene to give 2-heptyl-6-methoxybenzoate (712). Using a three-step sequence, the methoxy-carbonyl group of compound 712 was transformed to the methyl group present in the natural product. 3-Heptyl-3-methylanisole (713) was obtained in 85% overall yield. Finally, the anisole 713 was transformed to the arylamine 708 by nitration and subsequent catalytic hydrogenation. This simple sequence provides the arylamine 708 in six steps and with 26% overall yield (597,598) (Scheme 5.66). 

Another early success of the (TpRe(CO)(MeIm) fragment was the promotion of Diels-Alder cycloaddition reactions with benzene and anisole. Complex 101 [TpRe(CO)(MeIm)( 2-benzene)] undergoes an endo-selective Diels-Alder reaction with N-methylmaleimide to afford the bound bicyclo[2.2.2]octadiene complex 102 in 65 % yield (Scheme 12) [40]. Oxidation of 102 yields the bicyclo[2.2.2]octadiene 103 and/or the bicyclo[2.2.2]octenone 104 depending upon the choice of oxidation conditions. 

Scheme 13. A TpRe(CO)(Melm) -promoted Diels-Alder reaction of anisole and N-methylmaleimide.

In normal Diels-Alder reactions benzene and naphthalene usually prove to be quite inert as dienes anthracene adds reactive dienophiles at the central ring. These results are entirely as expected on the basis of the aromaticity of the systems. By contrast, tetrazine diester and 3,6-bistrifluoro-methyltetrazine, due to their low-lying LUMOs and lower resonance energy, will react even with aromatic compounds as dienophiles (Scheme 41) benzene, toluene, anisole, Af,A -dimethylaniline, and methylthiobenzene (226) react at 140°C <81CZ342, 87AG(E)332>. In monosubstituted benzene... 

An improved synthesis of glutinosone (1) was also accomplished by Masamune and coworkers6 and this was based on procedure developed by Dastur7,8 for the synthesis of sesquiterpenes nootkatone. (Scheme 2) Diels-Alder reaction of 3,6-dihydro-3,5-dimethyl anisole with methyl acrylate in absence of Lewis acids afforded a 1 3 mixture of esters (17) and (18) which were converted to a,(3-unsaturated aldehydes (19) in 77% yield by oxidation with selenium (IV) oxide in dioxane. Wittig reaction of aldehydes under the usual condition yielded the dienes (20) in 63% yield which on being subjected to Grignard reaction with an excess of methyllithium produced tettiary alcohols (21) in quantitative yield. This on treatment with formic acid at room temperature gave bicyclic enone (22) and its formate (23) in 45% and 41% yield respectively. Formates (23) were hydrolyzed to enone (22) in 88% yield. 

Complexes of metal + ligand + protein or DNA can also catalyze the Diels Alder cycloaddition or oxidations with hydrogen peroxide. Copper complexes bound to DNA catalyzed the Diels-Alder cycloaddition with up to 99% ee [15, 16], Cu(phthalocyanine) complexed to serum albumin also catalyzed the enantioselective (98% ee) Diels-Alder reaction, but only with very high catalyst loading (10 mol%) and only with pyridine-bearing dienophiles (presumably to complex the copper) [17]. Achiral Cr(III) complexes or Mn(Schiff-base) complexes inserted into the active site of apomyoglobin variants catalyzed the sulfoxidation of thio-anisole with up to 13 and 51% ee, respectively [18, 19]. A copper phenanthroline complex attached to the adipocyte lipid-binding protein catalyzed the enantioselective hydrolysis of esters and amides [20]. 

Anionic polymerization MA mechanism, 255-258 MA monomer, 239, 254-258 Anisole, 278 MA CTC, 210 Anthracene, 248, 254 acyla tion with MA, 94, 98 deutrated, MA Diels-Alder reaction, 137 MA CTC, 210... 

Fig. 18 The formation of a para-methoxystyrene complex from anisole and its use in Diels-Alder cycloaddition reactions...

Bauld, N. L., and Yang, J. "Stereospecificity and Mechanism in Cation Radical Diels-Alder and Cyclobutanation Reactions." Org. Lett, X 773-774 (1999). Gao, D., and Bauld, N. L. Mechanistic Implications of the Stereochemistry of the Cation Radical Diels-Alder Cycloaddition of 4-(cis-2-Deuteriovinyl)anisole to 1,3-Cyclopentadiene." /. Org. Chem., 65,6276-6277 (2000). Saettel, N. J., Oxsgaard, J., and Wiesl, O. "Pericyclic Reactions of Radical Cations." Eur. /. Cftem., 1429-1439 (2001). 

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