Heterocyclics benzodioxanes

Commensurately with the development of various catalyst systems, the Pd-catalyzed G-O cross-coupling has found a number of synthetic applications. Examples include the syntheses of the protein kinase G (PKC) activator (+)-decursin,104 the natural product heliannuol E,105 a chiral 2-methyl chroman,106 and a series of aryloxy and alkoxy porphyrins.107 The Buchwald-Hartwig coupling has also been utilized in the preparation of a heterocycle library.108 Intramolecular O-arylation has also been achieved in the reactions of enolates with aryl halides leading to benzofur-ans.109,110 Finally, a double cross-coupling between an 0-dibromobenzene and a glycol has also been applied for the preparation of benzodioxanes (Equation (16)).1... 

A tandem palladium-catalyzed reaction can effect a similar transformation to produce 2-vinyl-substituted heterocyclic systems as in Eq. 8E.11. By varying the amino acid moiety of the ligand, 83% ee could be obtained from the use of the glycine-derived ligand 129 [161]. A maximum enantioselectivity of 65% ee has been recorded for this type of reaction in an earlier study with BINAP as ligand [ 162]. Because both ( )- and (Z)-isomers gave the same enantioselectivity, attack on the rapidly interconverting 7t-allyl intermediates seems to determine the selectivity. Modest enantioselectivities have been reported for the related asymmetric preparation of 2-vinylpiperazine and 1,4-benzodioxane derivatives [163,164],... 

Amoldi A, Amone A, Merlini L (1984) Synthesis of the Natural Coumarinolignoids Propa-cin and Cleomiscosin A and B. An Empirical Spectroscopic Method to Distinguish Regioi-somers of Natural Benzodioxane Lignoids. Heterocycles 22 1537... 

Buchwald et al. demonstrated that the intramolecular palladium-catalyzed C—O bond formation was an attractive means to assemble the oxygen heterocycles 557 (Scheme 170).243 They applied this methodology to the synthesis of MKC-242 (560), a benzodioxane antidepressant (Scheme 171).243b... 

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