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Oxidation of Silyl Enol Ethers by Using IBX and IBX⋅N-Oxide Complexes: A Mild and Selective Reaction for the Synthesis of Enones

“…discovery and evolution of IBX ¥ N-oxide complexes and their use in the dehydrogenation of ketones and aldehydes at ambient temperature. [9] We have postulated that these IBXmediated dehydrogenation reactions [4,7,9] proceed through enolization (facilitated by the reagent) with concomitant capture of the enolate moiety, followed by single electron transfer (SET) to IBX and rearrangement of the resulting radical cation to give the a,b-unsaturated carbonyl compound. [7] This assessment led us to speculate that silyl enol ethers might undergo a similar oxidation with IBX, which would be a new, complimentary oxidation method for the synthesis of the much coveted enone functionality (Scheme 1 A).…”

“…The CH 2 Cl 2 content was always minimized, as its use as a cosolvent retards the reaction. [4,23] The solution was stirred vigorously, and progress was monitored by means of thin-layer chromatography. Upon completion, the reaction mixture was diluted with aqueous NaHCO 3 (5 %) and extracted with diethyl ether (3 Â ).…”

HIO3 and I2O5: Mild and Selective Alternative Reagents to IBX for the Dehydrogenation of Aldehydes and Ketones

“…[7] Armed with this information, we were able to tune the reactivity at the iodine nucleus by using a variety of Noxide ligands, and hence developed a mild room-temperature variant of the original IBX dehydrogenation with expanded functional group tolerance. [12] With such dramatic changes in reactivity patterns on changing the ligand from THF [7,8] or DMSO [10,11] to an N-oxide, [12,13] we began to question the role of all the substituents on the iodine nucleus, including the aromatic core. Herein we report initial results that probe the latter question and provide us with a number of economic, commercially available, and safe iodine(v) dehydrogenation agents whose structures contain no aromatic moiety.…”

“…These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: ( 44) 1223-336-033; or deposit@ ccdc.cam.ac.uk). [7] Thermal analyses were carried out using a TA-SDT 2960 apparatus at a heating rate of 5 K min À1 from 20 to 1000 8C under a flux of nitrogen: 6.8505 mg of the sample 1 and 11.9348 mg 2 were used for the measurement. To determine the role of the aryl moiety in the reactivity of IBX, we evaluated the most simple iodine(V)-based reagents: HIO 3 (1, iodic acid, IA) and its anhydride I 2 O 5 (2, iodine pentoxide, IP) (Scheme 1 B).…”

New Synthetic Technology for the Construction of N-Containing Quinones and Derivatives Thereof: Total Synthesis of Epoxyquinomycin B

“…[1] The inclusion of a nitrogen functionality within these unique systems, as in aminoquinone derivatives, enhances their versatility as building blocks for the construction of biologically relevant compound libraries and qualifies them as potential precursors to numerous naturally occurring substances. [2] Herein we report a facile process by which N-substituted p-quinones and o-azaquinones can be obtained regioselectively and in one step from readily available anilides by double functionalization of the aromatic nucleus (Scheme 1), and describe various applications of the resulting products including a short and efficient total synthesis of the naturally occurring anti-inflammatory agent epoxyquinomycin B (20, Scheme 4).Based on mechanistic insights gained during the study of the reaction of anilides with DMP (for abbreviations of reagents and protecting groups, see legends to schemes) described in the preceding communication, [3] we contemplated the possibility of an Ac-IBX molecule attacking intermediate II (Scheme 1) to give complex III, whose collapse in the presence of base was expected to form p-quinones (IV). Indeed, a small amount of 18 O-labeled p-quinone was detected upon exposure of a substituted anilide to two equivalents each of DMP and Ac-IBX-18 O.…”