Oxidative-cyclization

Rosenow, M. A., Huffman, H. A., Phail, M. E., and Wachter, R. M. (2004). The crystal structure of the Y66L variant of green fluorescent protein supports a cyclization-oxidation-dehydration mechanism for chromophore maturation. Biochemistry 43 4464 1472. 

Reaction of commercially available 3-chlorotetronic acid 762, obtained by pyrolysis of methyl 2,4-dichloroacetoacetate at 140 °C in vacuo [235], with o-phenylene-diamine affords, after cyclization-oxidation with AgOAc, the quinoxaline lactone 763 in 69% yield [234] (Scheme 5.83). 

Scheme 2.219. Base-promoted cyclization/oxidation reaction of compounds 2-974.

The addition of a carbonylation step extended a pyrrole synthesis to pyrrole-2-acetic acid derivatives <06ASC2212>. Treatment of enyne amine 1 with palladium diiodide in the presence of CO and methanol produced pyrrole-2-acetic ester 2 via a 5-exo-dig cyclization, oxidative carbonylation, and isomerization. 

Quinoxaline 1-oxide (209) reacts with phenyl isocyanate to give 2-anilinoquinoxaline (210) together with 1,3-diphenyl-l-(2-quinoxalinyl)-urea (211) and cyclized oxidation product of the urea 212.215 2-Quinoxalinone 4-oxide (205) and its 1-methyl derivative undergo addition reactions, e.g., with phenyl isocyanate and benzyne to give compounds 214 and 216, respectively.216 These reactions are formulated as proceeding via the intermediate cycloadducts 213 and 215. Compound 216 has also been obtained by photolysis of 3-(o-hydroxy-phenyl)quinoxaline 1-oxide.51 1,3-Dipolar cycloaddition of quinoxaline... 

As is true for other classes of aromatic nucleophilic substitution, the halogen displacement can frequently be catalyzed by copper or copper(I) salts. Using sodium hydride as the base and copper(I) iodide as catalyst, a series of o-bromophenylethylamine derivatives, including both amides and carbamates, have been cyclized. Oxidation to the indole can be effected with manganese dioxide (81JCS(P1)290). 

A novel one-pot tandem oxidation-cyclization-oxidation process was successfully applied in the transformation of unsaturated alcohols 250 [Eq. (5.315)].860 The intermediate aldehyde formed by oxidation with pyridinium chlorochromate (PCC) undergoes a carbonyl-ene cyclization followed by an additional oxidation to form 3-substituted piperidinones. 

On heating the condensed [l,2,4]-triazolo[4,3- ]pyridazine-6(577)-one-3(27/)-thione 91 with dialkyl acetylenedi-carboxylates in DMF, the subsequent ring transformations yielded the novel tetracyclic 1,3-diazepine cis-92, which can further be converted to 93 in a number of steps involving elimination, decarboxylation, and cyclization oxidation upon heating (Scheme 15) <2001T7191>. 

Positions engaged in cyclization Oxidant consumed (moles) Formaldehyde produced (moles) Formic acid produced (moles)... 

The synthesis of the limondd azadiradione, utiiizing a Hg° cyclization-oxidative demercuration sequence with an enol phosphate derived from trans,trans-famesol has been reported. Azadiradione, a te-tracarbocyclic memter of the iimonoid group isoiated from the neem tree, Azadirachta indica, has been converted to other tetracyclic limonoids, and is thus a key intermediate. The sequence is shown in Scheme 33. 

Benzohydrofuranes. 2-Allylphenols are cyclized oxidatively by Pd(OAc)2 (1 equiv.) to isomeric benzofuranes. In the presence of oxygen, the Pd(II) salt can be used in catalytic amounts. An example is formulated in equation (I). ... 

The previous examples rehed on a radical termination. Cationic termination could also be used, after suitable oxidation of the final radical (Scheme 75) [211]. Thus, ester 252 was treated with base and ethylchloro-formate to give anion 253, which was oxidized to malonyl radical 254 by the ferrocenium ion. Cyclization/oxidation gave cation 256, which yielded 93% of malonate 257 by loss of the TMS group. This adduct was further elaborated upon and led to a cyclopentanoid monoterpene, dihydronepetal-actone. 

This type of stereocontrol is featured in a synthesis of the fungitoxin ( )-chokol-A (156) (Scheme 32). Alcohol (147) (easily prepared from l-hexen-5-one in two steps) efficiently gave the allyl chloride (148) (CCI4/PBU3). The metallation/cyclization/oxidation step (148) - (l49) -> (150) (151) (de-... 

In an alternative two-step transformation of 5-spirocyclopropane isoxazolidines to tetrahydropyridones, for example, 7-amino cyclopropanol 214, prepared by chemoselective N-O reduction of isoxazolidine 213, was converted into 215 by treatment with Cu(OAc)2 and LiOAc in the presence of catalytic amounts of Pd(OAc)2. Interestingly, 7-amino cyclopropanols can also undergo a Pd-catalyzed domino ring-opening/cyclization/oxidation process to afford dihy-dropyridones such as 216 when the reaction is carried out in the presence of air or O2 (Scheme 49) <2005JOC5636>. 

Pyrrolo[l,2-a]indoloquinones of the mitosene type (31) were prepared by either oxidation or cyclization. Oxidation of amino or hydroxy precursors was done mainly with Fremy s salt (72ABC106 73TL131 74ABC381, 74JOC3580 85LA1422). 

The most obvious pathway from acetate involves polyketide assembly, some sort of cyclization, oxidation of the methyl group, and oxidation of the ring. Again, you may have chosen a different order of events from ours or even a different pathway. 

Pseudosolasodine diacetate (204), derived as the first degradation product of soiasodine, reacts quantitatively with iodine. Chromatography of the solution on silica gel gave the product (205) of 23,Ai-cyclization. Oxidation by the usual... 

Some halogenated 2-pyrazolin-5-ones have been prepared by cyclization of various aliphatic compounds. Darapsky, Berger and Neuhaus353 have treated a /J-hydrazino hydrazide with bromine to achieve cyclization, oxidation and halogenation in one step (eq. 207). 

Similar to the nickel-catalyzed reactions, metallacycles of palladium are assumed to be intermediates of these conversions. They were isolable in some cases. Thus, 3,3-dimethylcyclopropene with -allyl( ) -cyclopentadienyl)palladium, on cyclizing oxidative addition, formed metallacyclopentanes 20 and metallacyclononanes 21, depending on the reaction conditions. Thermal decomplexation via reductive elimination gave cyclopropane systems and products thereof. ... 

By contrast, no diastereoselectivity was found in the type II magnesium-ene cyclization/oxidation (158) (159) (160), which afforded the carrion beetle defense compound P-necrodol (160a) together... 

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