Hypervalent-iodine-mediated tandem

The hypervalent-iodine-mediated tandem reaction process, reported for preparation of benzodiazepinones, when applied to 2-hydroxy-AT-arylben-zamides 92 afforded dibenzo[d,/][l,3]oxazepin-6(7fi)-ones 93 (14AGE6216). 

If the oxidation is performed in the presence of an external dienophile, the respective products of [4+2] cycloaddition are formed [351-356]. Typical examples are illustrated by a one-pot synthesis of several silyl bicyclic alkenes 283 by intermolecular Diels-Alder reactions of 4-trimethylsilyl substituted masked o-benzoquinones 282 generated by oxidation of the corresponding 2-methoxyphenols 281 [351] and by the hypervalent iodine-mediated oxidative dearomatization/Diels-Alder cascade reaction of phenols 284 with allyl alcohol affording polycyclic acetals 285 (Scheme 3.118) [352]. This hypervalent iodine-promoted tandem phenolic oxidation/Diels-Alder reaction has been utilized in the stereoselective synthesis of the bacchopetiolone carbocyclic core [353]. 

Additional examples of synthetic applications of hypervalent iodine-induced heterocyclizations include the following the metal-free one-pot synthesis of 2-acylbenzothiazoles by oxidative cyclization of multiform substrates [434], iodine(III)-mediated tandem oxidative cyclization for construction of 2-nitrobenzo[ ]furans [435], hypervalent iodine mediated oxidative cyclization of o-hydroxystilbenes into benzo- and naphthofu-rans [436], PhI(OCOCF3)2-mediated synthesis of 3-hydroxy-2-oxindoles and spirooxindoles from anilides [437], synthesis of isoxazoles by hypervalent iodine-induced cycloaddition of nitrile oxides to alkynes [438],... 

W. Liu, P. Zhou, C. Chen, Q. Zhang, Z. Zhu, Direct construction of 5-methyl-2-phenylisoxazol-3(2H)-ones via hypervalent iodine mediated sequential tandem oxidative cyclization of 3-oxo-N-phenylbutanamides catalyzed by zinc oxide, Org. Biomol. Chem. 11 (2013) 542-544. 

Canesi and coworkers have developed several synthetically useful tandem rearrangements on the basis of hypervalent iodine-promoted phenolic oxidation [328-331]. An oxidative Prins-pinacol tandem process mediated by a hypervalent iodine reagent allows the stereoselective tfansformation of simple phenols 261 into highly elaborate spirocyclic dienone cores 262 containing several quaternary carbon centers (Scheme 3.108). 

An oxidative Prins-pinacol tandem process mediated by hypervalent iodine reagent was recently established by the Canesi group [93] and it was used for the formal synthesis of (-)-platensimycin (Scheme 14) [94]. The strategy allowed rapid access to the highly functionahzed spirocyclic core present in the target natural product. 

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