Indium triflate-assisted nucleophilic aromatic substitution reactions of nitrosobezene-derived cycloadducts with alcohols

Oxidative Dearomatization of Pyridines

Dearomatization of pyridines is a well-established synthetic approach to access piperidines. Although remarkably powerful, existing dearomatization processes have been limited to the hydrogenation or addition of carbon-based nucleophiles to activated pyridiniums. Here, we show that arenophile-mediated dearomatizations can be applied to pyridines to directly introduce heteroatom functionalities without prior substrate activation. The arenophile platform in combination with olefin oxidation chemistry provides access to dihydropyridine cis-diols and epoxides. These previously elusive compounds are now readily accessible and can be used for the downstream preparation of diversely functionalized piperidines.

Passerini-Smiles Reaction of α-Ketophosphonates: Platform for Phospha-Brook/Smiles Embedded Cascades

The Passerini-Smiles reactions of α-ketophosphonates with nitrophenols has been used as a platform to observe complex cascades involving multiple Smiles transfers coupled with phospha-Brook rearrangement. When using 4-nitrophenols a rare 1,3-Truce-Smiles rearrangement is observed leading to diarylacetamide derivatives. 2-Nitro-derivatives lead to a completely different reactivity pattern that may be explained by a nitro to nitroso conversion followed by a σ-π metathesis. All mechanistic assumptions are confirmed by DFT calculations performed on both families of adducts. The potential of this work has been further demonstrated by the use of N-aryl α-ketoamides as alternative starting materials for these cascades as well as the disclosure of new aza-Nazarov access to hydroxy-indolones.

Facile access to [1,2]-oxazine derivatives via annulations of aminoxy-tethered 1,7-enynes

An efficient approach for the highly diastereoselective construction of functionalized cyclopenta[d][1,2]oxazines via sequential oxyamination and Pauson-Khand reaction of readily accessible propargylic alcohols has been developed. Furthermore, the ring closing metathesis of these N-O linked 1,7-enynes afforded vinylated-[1,2]oxazines in good yields. The reduction of the N-O bond of the obtained cyclopenta[d][1,2]oxazine is accomplished to access cyclopentenone-based amino alcohols.

Copper-Catalyzed Aqueous N-O Bond Cleavage of 2-Oxa-3-Azabicyclo Compounds to Cyclic cis-1,4-Amino Alcohols

The N-O bond cleavage of 2-oxa-3-azabicyclo substrates, which are readily prepared by the hetero Diels-Alder reaction between nitroso dienophiles and cyclic 1,3-dienes, was effectively catalyzed by heterogeneous copper-on-carbon (Cu/C) under aqueous conditions to give the corresponding cyclic cis-1,4-amino alcohol derivatives. The present method was applied to the direct incorporation of the hydroxy and amino groups derived from a nitroso substrate into cyclic 1,3-dienes with cis-selectivity by the combination of the in situ formation of 2-oxa-3-azabicyclo compounds and following Cu/C-catalyzed N-O bond cleavage. The obtained cis-4-aminocyclohexenols, derived from cyclohexadiene as a cyclic 1,3-diene, could be selectively oxidized by using the ruthenium-on-carbon (Ru/C) catalyst under oxygen atmosphere to the corresponding 4-aminocyclohexenones at 50-65 °C or para-iminoquinones at 100-110 °C as useful reactive synthetic precursors.

K2CO3-Mediated Cyclization and Rearrangement of γ,δ-Alkynyl Oximes To Form Pyridols

A novel K₂CO₃-mediated cyclization and rearrangement of γ,δ-alkynyl oximes for the synthesis of pyridols is described. The process accomplishes an efficient [1,3] rearrangement of the O-vinyl oxime intermediate which is in situ generated from the intramolecular nucleophilic addition of γ,δ-alkynyl oximes. The reaction employs readily accessible starting materials, tolerates a wide range of functional groups, and gives a variety of synthetically challenging pyridols in good yields.

Developing nitrosocarborane chemistry

New nitrosocarboranes or their hydroxylamine or Diels–Alder cycloadducts have been prepared and fully characterised.

Fe-Catalyzed reductive NO-bond cleavage – a route to the diastereoselective 1,4-aminohydroxylation of 1,3-dienes

We describe the iron-catalyzed reductive cleavage of N–O-bonds in oxazines using malononitrile as reductant, which – in sequence with a [4 + 2]-cycloaddition – can be considered as an efficient way for the diastereoselective 1,4-aminohydroxylation of 1,3-dienes.

Theoretical analysis of reactivity patterns in Diels-Alder reactions of cyclopentadiene, cyclohexadiene, and cycloheptadiene with symmetrical and unsymmetrical dienophiles

The Diels-Alder reactions of cyclopentadiene, cyclohexadiene, and cycloheptadiene with a series of dienophiles were studied with quantum mechanical calculations (M06-2X density functional theory) and analyzed with the distortion/interaction model. The poor reactivities of cyclohexadiene and cycloheptadiene with dienophiles that give relatively synchronous transition states result from the substantial distortion required to achieve a transition state involving the formation of two bonds of the diene simultaneously. However, highly asynchronous or stepwise reactions result in less distortion of the diene and less differences in reactivities of different dienes. The transition state geometry of cyclopentadiene is less distorted in the asynchronous reaction with 1,1-dicyanoethylene compared to that with cis- and trans-1,2-dicyanoethylenes, which react through synchronous transition states.

Synthesis of protected (1-phenyl-1h-pyrrol-2-yl)-alkane-1-amines from phenylnitroso Diels-Alder adducts with 1,2-dihydropyridines

The reductive cleavage of nitrosobenzene-derived cycloadducts with appropriately protected 1,2-dihydropyridines allows a novel and simple obtainment of substituted N-[1-(1-phenyl-1H-pyrrol-2-yl)alkylamides. This synthesis can also be carried out in a very simple, mild, and practical one-pot procedure without isolation of the corresponding nitrosobenzene cycloadduct by means of catalytic amounts of CuCl.

[4 + 2] Cyclocondensation reactions of tungsten-dihydropyridine complexes and the generation of tri- and tetrasubstituted piperidines

A new method for the preparation of functionalized piperidines is described in which various dihydropyridine (DHP) complexes of {TpW(NO)(PMe(3))} that are derived from pyridine-borane undergo [4 + 2] cyclocondensation with enones, enals, nitrosobenzene, and several isocyanates to form [2.2.2] bicyclic species. In several cases the diazabicyclooctene products derived from DHP complexes and isocyanates can be further elaborated into novel syn-2,5-disubstituted and 2,3,6-trisubstituted piperidinamides.