Microwave-Assisted Cp*Co^III-Catalyzed C–H Activation/Double C–N Bond Formation Reactions to Thiadiazine 1-Oxides

Abstract

A microwave-assisted, Cp*Co-catalyzed direct C-H activation/double C-N bond formation reaction of simple NH-sulfoximines with 1,4,2-dioxazol-5-ones to produce diverse thiadiazine-1-oxides is reported. The reaction tolerates a broad range of functional groups under external oxidant-free conditions and only releases CO and HO as the sole byproducts. The preliminary mechanistic studies revealed an electrophilic metalation pathway is likely involved in the reaction.

Katalytische Umwandlung von funktionalisierten cyclischen organischen Carbonaten

“…Transformation von 1,4,2-Dioxazol-5-onen 1,4,2-Dioxazol-5-one (Dioxazolone,c yclische Nitrilcarbonate) sind aufgrund ihrer schwachen N-O-Bindung bei milden Bedingungen leicht zu aktivieren. Aufd iese Weise konnten Chinazoline [60] und ihre N-Oxide, [61] Benzimidazolene, [62] Azolopyrimidine [63] und Thiadiazin-1-oxide [64] in einem Syntheseschritt hergestellt werden. Als besonders geeignet zeigten sich diese Substrate bei Reaktionen, die die C-H-Amidierung von (Hetero)Arenen beinhalten (Schema 19).…”

IronIII‐catalyzed Chemoselective Cycloaromatization Reactions for the synthesis of 5‐Brominated Benzo[b]fluorenones

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 Inspired by the fascinating role of transition-metals in the synthesis of carbo/heterocyclic molecules, we hypothesized the reactivity of the ortho-alkynyllphenyl ynones 1 could still be activated in proper catalytic conditions. However, the coinage-metal catalysts, such as AgOTf, AgBF 4 and Ph 3 PAuCl/AgSbF 6 , which were utilized in our previous cycloisomerization reactions of 1,6-diynols with NXSs, [13] can only produced low to modest yields of the desired products (entries [16][17][18][19]. Finally, a smooth conversion was observed when Fe(OAc) 2 was utilized, and the desired product 2 a could be isolated in 62% yield in a shorter reaction time (entry 11).…”

“…In the reaction of NCS, the conversion was very slow, an unknown compound was isolated in low yield, whereas no desired chlorinated benzo[b]fluorenone was detected. Moreover, when one equivalent of a typical radical scavenger, [18] such as BHT, styrene or TEMPO, was added individually as an additive under the standard conditions, the corresponding reactions were not obviously suppressed. In addition, Selectfluor was added into the raction in order to prepare the fluorinated analogues, however, no positive result was obtained.…”

“…Interestingly, a comparable reaction was observed when Mg(OTf) 2 (10 mol%) was used as a catalyst, and the desired product 2 a was isolated with a 65% yield in 5 h (entry 15). However, the coinage-metal catalysts, such as AgOTf, AgBF 4 and Ph 3 PAuCl/AgSbF 6 , which were utilized in our previous cycloisomerization reactions of 1,6-diynols with NXSs, [13] can only produced low to modest yields of the desired products (entries [16][17][18][19]. Screening of the reaction solvents showed that ethyl acetate (EA) was a suitable reaction medium, and the yield of 2 a could be improved up to 89% (entries 20-23).…”

Iridium‐Catalyzed Regio‐ and Stereoselective C‐H Oxidative Reaction to (Z)‐3‐Arylidene‐2‐oxindole Imides under Neutral Conditions

“…Although the allylidenyl imine moiety (C=NTs) in product 3 a seemed very stable under a high-temperature hydrol- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 ysis environment even in Lewis acid-catalyzed oxidative condition (table 1, entry 5), this imine moiety could be successfully hydrolyzed under a Brønstedacid promoted reaction. When typical radical scavengers, [22] such as TEMPO, BHT and styrene were added, the corresponding product 3 a could be isolated in moderate to good yields (37-62% yields, respectively, Scheme 4), indicating the radical-process should be most possibly 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 excluded in this oxidative transformation. 1).…”