Simple access to pentacyclic oxazinoisoquinolines via an unexpected transformation of aminomethylnaphthols

Unexpected reactions between 1-α-aminobenzyl-2-naphthol, 1-aminomethyl-2-naphthol, N-benzyl-1-α-aminobenzyl-2-naphthol and 6,7-dimethoxy-3,4-dihydroisoquinoline to furnish naphth[1,2-e][1,3]oxazino[2,3-a]isoquinolines are reported. The reaction conditions involved classical heating at 80 °C in MeCN for 22 h (57-62%), or the use of microwave conditions (100 °C), which allowed a reduction of the reaction time to 90 min and resulted in somewhat higher yields (73-82%).     

An unexpected transformation of benzyl carbamates into α-azidobenzeneacetamides

Successive treatment of benzyl carbamates 5 (Z-protected secondary amines) with lithium diisopropylamide (LDA), diphenyl phosphorochloridate (DPPC1), and NaN 3 yielded the corresponding ã-azidobenzeneacetamides 6 in 45–50% yield (Schemes 2 and 3). In the case of Z-protected diisopropylamine 5b , the phosphate 7 was isolated as a minor product. A reaction mechanism for this unexpected transformation is proposed in Scheme 4, the key step being the ring closure of a benzylic anion to give an oxirane intermediate B. In cursory experiments, it was demonstrated that ã-azidobenzeneacetamides 6 can be used as 2-phenylglycine synthons in the formation of dipeptides by using a phosphine-mediated coupling (Scheme 5).     

Thio-functionalised glucosinolates: unexpected transformation of desulfoglucoraphenin

Enzymatic desulfation of stable glucoraphenin affords desulfoglucoraphenin, which unexpectedly undergoes further transformations into cyclic nitrone-type derivatives.     

An unexpected aminocyclopropane reductive rearrangement

A reductive rearrangement of aminocyclopropanes is described for the synthesis of cis- or trans-fused bicyclic 1,2-diaminocyclobutanes. Ionization of a cyclic aminal using BF₃·OEt₂ induces rearrangement to a cyclobutyl iminium ion, which is subsequently reduced by Et₃SiH. Substitution with allyltrimethylsilane allows carbon incorporation, giving a quaternary center. Silyloxy-substituted cyclopropanes rearrange rapidly to cyclobutanones which react with NaBH₄ to provide 1,2-aminohydroxycyclobutanes. These aminals were generated by the reduction of a Boc-imide with DIBAL-H or LiBH₄.     

An unexpected result in an intramolecular Ritter reaction induced by triflic anhydride

The treatment of the methyl 2-(cyanoethyl)-1-hydroxy-2-indane-carboxylate 1b in dichloromethane solution with triflic anhydride at 20°C afforded the tricyclic enone 3 in 65% yield, instead of the expected lactam 2b produced under the ‘classic’ conditions of the Ritter reaction.     

An unexpected synthesis of ketene monothioacetals

Some dithiocarbonates (xanthates) can be converted into ketene monothioacetals through extrusion of sulfur upon treatment with base and an alkylating agent.     

An unexpected base-induced rearrangement of tritylamine

An unexpected rearrangement was observed during the treatment of tritylamine with n-butyllithium, leading to the formation of an imine.     

Autohetarylation of 4,6-dimethyl-5-nitro-2chloro-3-cyanopyridine — An unexpected transformation in the presence of bases

Under the influence of bases, the 4-6-dimethyl-5-nitro-2-chloro-3-cyanopyridine molecule was found to undergo autohetarylation with the formation of a doubled molecule. Based on RSA data, it was found that such a process takes place exclusively at the methyl group in the 4 position.M. V. Lomonosov Moscow State University, Moscow 119899. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 680–684, May, 1996.     

Aromatic ortho-benzylation reveals an unexpected reductant

The discovery of a novel arylpalladium(II) reduction enables the synthesis of diarylmethanes via reductive benzylation. Benzyl chlorides were found to be the major source of hydride, acting as an alkylating agent and an aprotic surrogate for benzyl alcohol. This represents the first example of an arylpalladium(II) reduction mediated by a benzyl halide.     

An unexpected product from attempted reductive etherification of a silyl alcohol with an aldehyde

Reductive etherification, using BiBr₃/Et₃SiH, between two modified amino acids, one with a silyl alcohol side chain and one with an aldehyde side chain, gave, not the desired bis-amino acid, but a tetrahydrooxazine, in good yield.     

An unexpected cyclization path to some pyrazoles

The treatment of ketal hydrazones of arylglyoxals (2) with 75% sulfuric acid leads to 3-aroyl-4-phenyl-1-methylpyrazoles (6) as well as 4-phenyl-1-methylpyrazole (7) and the corresponding benzoic acids. Possible mechanisms are discussed.     

Novel stereochemistry, reactivity, and stability of an arsenic heterocycle in a metal-promoted asymmetric cycloaddition reaction

The organopalladium complex containing ortho-metalated (S)-[1-(dimethylamino)ethyl]phenylene as the chiral auxiliary has been used as the chiral template to promote the asymmetric cycloaddition reaction between diphenylvinylphosphine and 3,4-dimethyl-1-phenylarsole. A diphenylphosphino-substituted asymmetrical heterobidentate arsanorbornene (As-P) ligand was obtained stereoselectively on the chiral palladium template in moderate yield. The chiral benzylamine auxiliary could be removed chemoselectively from the template by treatment with HCl to produce the neutral complex [(As-P)PdCl2]. In contrast to their reported P-P analogue, the arsenic donor in the dichloro complex could be eliminated stereospecifically under mild reaction conditions to generate the corresponding 1-(diphenylphosphino)-3,4-dimethyl-2,4-cyclohexadiene, which remained as a bidentate ligand at the PdCl2 unit via phosphorus and the eta2-C4-C5 double bond. The arsenic-elimination process was found to be influenced by the halo ligand in [(As-P)PdX2]. A similar process was observed with the analogous dibromo complex, but the corresponding diiodo species did not show similar reactivity. All of the novel As-Pd complexes have been characterized by X-ray crystallography.     

An unexpected Diels-Alder reaction on the fullerene core rather than an expected 1,3-dipolar cycloaddition

Fullerene derivatives resulting from an unexpected Diels-Alder cycloaddition have been obtained by reaction of trans-2-stilbenecarboxaldehyde derivatives with N-methylglycine and C60.     

An unexpected base-induced [1,4]-phospho-Fries rearrangement

An unexpected [1,4]-phospho-Fries rearrangement that gives rise to the formation of a O,O,O,O-tetraethyl methylenebis(thiophosphonate) derivative is reported. The regioselectivity of the metallation with n-BuLi or t-BuLi is the key factor that explains either the [1,4] or [1,3] rearrangement observed.     

Regulation of excitation transitions by molecular design endowing full-color-tunable emissions with unexpected high quantum yields for bioimaging application

Organic fluorophores are indispensible in chemical/biological imaging. The conjugated fluorescent molecules simultaneously possessing highly tunable emission, high quantum yield in solvents of different polarities, and large Stokes shift are quite rare. Herein, we report a new category of fluorophores based on diarylated thieno[3,4-b]thiophenes efficiently synthesized by direct C–H arylation reaction. TbT-Fluors showed full-color-tunable emissions with large Stokes shifts. Intriguingly, the fluorescence quantum yields of TbT-Fluors are barely sensitive to solvent polarities, approaching 100%. Based on photophysical and theoretical investigations, we found that the enhanced oscillator strength of the S₁-S₀ transition and increased T₂-S₁ energy difference can sufficiently compensate the negative effect from the decreased energy gap and increased reorganization energy in dimethyl sulfoxide (DMSO). Bioimaging applications revealed that some TbT-Fluors can penetrate the cell membrane and are superior for imaging in terms of high photochemical stability and low cytotoxicity. Furthermore, TbT-PhF exhibits specific colocalization with mitochondria in living cells.