Imination of sulfoxides using 3-acetoxyaminoquinazolinone as nitrogen source in the presence of hexamethyldisilazane

The reaction of 3-acetoxyaminoquinazolinone (QNHOAc) with various sulfoxides in the presence of HMDS as an acetic acid scavenger, afforded the corresponding sulfoximides in good yields. Sulfoximidation of phenyl methyl sulfoxide using a Q*NHOAc having a stereogenic centre on its 2-position gave the products in 1.3:1 ratio of diastereomers.     

Hypoiodite-mediated metal-free catalytic aziridination of alkenes

Look, no metal: A metal-free catalytic procedure for aziridination of alkenes using tetrabutylammonium iodide as the catalyst, m-chloroperoxybenzoic acid (mCPBA) as the terminal oxidant, and N-aminophthalimide as the nitrenium precursor has been developed (see scheme; right: X-ray structure of one of the products). Control experiments suggests that the active oxidant is in?situ generated hypoiodous acid (HIO).     

NaIO4/LiBr-mediated aziridination of olefins using chloramine-T

A new milder protocol for aziridination of a variety of olefins has been described. The process employs catalytic amount of sodium metaperiodate (NaIO₄) as an oxidant and LiBr and chloramine-T as the bromine and nitrogen sources, respectively. Interestingly, the formation of aziridine products in all the cases studied takes place presumably through a process of 1,2-aminobromination of alkenes.     

An efficient transition metal-free aziridination of alkenes with Chloramine-T using aqueous H2O2/HBr

The combination of aqueous H₂O₂ and HBr was found to be an efficient transition metal-free green catalytic system for the aziridination of a variety of alkenes under very mild reaction conditions.     

Enantioselective aziridination of alkenes with N-aminophthalimide in the presence of lead tetraacetate-mediated chiral ligand

[reaction: see text] Reaction of various N-enoyl oxazolidinones 5a-f with N-aminophthalimide and lead tetraacetate in the presence of camphor-derived chiral ligands provides the desired N-phthalimidoaziridines 6a-f in good to high enantiomeric excess (67-95% ee) at 0 degrees C within 15 min. The absolute stereochemistry of the corresponding aziridine derivatives was established by chemical correlations.     

Substrate-controlled highly diastereoselective synthesis of primary and secondary diorganozinc reagents by hydroboration/boron-zinc exchange sequence

The scope of substrate-controlled diastereoselective hydroborations can be considerably enhanced by a boron-zinc exchange reaction, providing organozinc derivatives that react with a broad range of electrophiles. Even normally unreactive boronic esters, obtained by Rh-catalyzed hydroboration with catecholborane, react readily with iPr2Zn providing the corresponding zinc reagents in high diastereoselectivity.     

Formation of unexpected products in the attempted aziridination of styrene with trifluoromethanesulfonyl nitrene

The reaction of styrene with trifluoromethanesulfonyl nitrene generated from trifluoromethanesulfonamide in the system (t-BuOCl+NaI) results in the formation of trifluoro-N-[2-phenyl-2-(trifluoromethylsulfonyl)aminoethyl]methanesulfonamide, 1-phenyl-2-iodo-ethanol, and 2,5-diphenyl-1,4-bis(trifluoromethylsulfonyl)piperazine rather than the expected product of aziridination, 2-phenyl-1-(trifluoromethylsulfonyl)aziridine. The mechanism of the reaction is discussed.     

Palladium(II) mediated aziridination of olefins with bromamine-T as the nitrogen source: scope and mechanism

The palladium(II)-promoted reaction of a variety of olefins and bromamine-T provided N-tosyl-2-substituted aziridines under mild conditions. Olefins bearing chiral appendages gave only a poor to modest diastereoselectivity. Appropriate deuterated olefins were selected to study the stereochemistry of the reaction. A Pd(IV) intermediate is proposed as the aziridinating species.     

Asymmetric catalytic aziridination of dihydronaphthalenes for the preparation of substituted 2-aminotetralins

An enantioselective synthesis of substituted 2-aminotetralins from dihydronaphthalenes in four steps is described. The key step is the Jacobsen’s (diimine)copper-catalyzed asymmetric aziridination of dihydronaphthalenes to the respective aziridines in 33-82% yields and 60-87% enantiomeric excess. The enantioselectivity and the yield were dependent on the properties of the nitrene precursor. pTsNIPh appeared in general to give better results than pNsNIPh. Aziridines were ring-opened in the benzylic position by catalytic hydrogenolysis in quantitative yields, and deprotected in two steps to the respective 2-aminotetralins in 66-85% yields. The synthesis of (S)-2-aminotetralin (>98% ee) and (S)-2-amino-7-methoxytetralin (56% ee) were accomplished in 30 and 52% overall yields, respectively.     

One-pot reaction of 2-formylbenzoates,hexamethyldisilazane, and diethyl phosphite in the presence of Yb(OTf)3: Synthesis of 3-phosphonate phthalides

Reaction of 2-formylbenzoates with hexamethyldisilazane and diethyl phosphite in the presence of Yb(OTf)₃ proceeded smoothly at room temperature to afford addition adducts, which were readily cyclized to 3-phosphonate phthalides by adding trifluoroacetic acid (TFA). The reactions employing Sc(OTf)₃ instead of Yb(OTf)₃ produced 3-phosphonate isoindolinones without addition of TFA.     

The mechanism of the (bispidine)copper(II)-catalyzed aziridination of styrene: a combined experimental and theoretical study

Experimental and DFT-based computational results on the aziridination mechanism and the catalytic activity of (bispidine)copper(I) and -copper(II) complexes are reported and discussed (bispidine=tetra- or pentadentate 3,7-diazabicyclo[3.1.1]nonane derivative with two or three aromatic N donors in addition to the two tertiary amines). There is a correlation between the redox potential of the copper(II/I) couple and the activity of the catalyst. The most active catalyst studied, which has the most positive redox potential among all (bispidine)copper(II) complexes, performs 180 turnovers in 30 min. A detailed hybrid density functional theory (DFT) study provides insight into the structure, spin state, and stability of reactive intermediates and transition states, the oxidation state of the copper center, and the denticity of the nitrene source. Among the possible pathways for the formation of the aziridine product, the stepwise formation of the two N-C bonds is shown to be preferred, which also follows from experimental results. Although the triplet state of the catalytically active copper nitrene is lowest in energy, the two possible spin states of the radical intermediate are practically degenerate, and there is a spin crossover at this stage because the triplet energy barrier to the singlet product is exceedingly high.     

Oxidative Allene Amination for the Synthesis of Azetidin‐3‐ones

Regioselectivity in the aziridination of silyl‐substituted homoallenic sulfamates is readily diverted to the distal double bond of the allene to yield endocyclic bicyclic methyleneaziridines with excellent stereocontrol. Subsequent reaction with electrophilic oxygen sources initiates facile rearrangement to densely functionalized, fused azetidin‐3‐ones in excellent d.r., effectively transferring the axial chirality of the allene to central chirality in the products. The steric nature of the silyl group dictates which of the two rings of the fused azetidin‐3‐one will undergo further functionalization, providing an additional element of diversity for the preparation of enantioenriched azetidine scaffolds with potential biological activity.     

One-pot enantioselective aziridination of olefins catalyzed by a copper(I) complex of a novel diimine ligand by using PhI(OAc)(2) and sulfonamide as nitrene precursors

A novel chiral C(2)-symmetric 1,4-diamine with multistereogenic centers at the backbone of the ligand has been synthesized from cheap natural product D-mannitol through multistep transformations. Its diimine derivative (3 a) was found to be highly effective for the enantioselective control of the copper-catalyzed asymmetric aziridination of olefin derivatives with PhI==NTs as the nitrene source, affording the corresponding N-sulfonylated azirindine derivatives in good to excellent yields with up to 99 % ee (ee=enantiomeric excess). The catalyst system discovered in the present work was also extended to a one-pot enantioselective aziridination by using sulfonamide/iodobenzene diacetate as the nitrene source. In this case, most reactions proceeded smoothly to give the corresponding products in moderate yields with good to excellent enantiomeric excesses (75-96 % ee).     

A direct efficient diastereoselective synthesis of enantiopure 3-substituted-isobenzofuranones

Condensation of (−)-8-benzylaminomenthol with o-phthaldehyde lead to the chiral perhydro-1,3-benzoxazine 2 as single diastereoisomer. That compound reacted with different organometallics leading to 3 in excellent de. Hydrolysis of carbinols, followed by oxidation of the intermediates allowed for the synthesis of enantiopure phthalides.     

A Model Study of Intramolecular Asymmetric Radical Cyclizations of α-Ester and α-Amide Radicals

Starting from malonate, a practical route was developed for the synthesis of α-phenylthio acid 3. Several chiral compounds including (-)-menthol, (-)-8-pbenylmenthol and a camphor based oxazolidinone 8 reacted with 3 to give α-phenylthio esters or amide. These sulfides cyclized efficiently when reacted with tributyltin hydride. Among the chiral auxiliaries used, 8-phenylmenthyl group displayed moderate asymmetric induction (64% ee for cis-product and 40% ee for trans-product). Based on this results, a transition state model was proposed to explain the observed stereoselectivity. In this model, due to π,π-orbital overlap of the phenyl ring and the carbonyl, the si-face of the most stable conformer of the radical was shielded. This controlled the carbon-carbon bond formation to occur from the re-face.     

The mechanism of the addition of tetrahaloalkanes to alkenes in the presence of RuCl2(PPh3)3

The addition of tetrahaloalkanes to alkenes in the presence of [RuCl₂(PPh₃)₃] has been examined in detail and it is suggested that it proceeds by a non-chain catalysed mechanism involving free radical intermediates.     

A highly diastereoselective [3+3] annulation reaction of aza-oxyallyl cations and nitrones

An efficient synthesis of 1,2,4-oxadiazinan-5-ones via [3+3] cycloaddition of in situ generated aza-oxyallyl cations with nitrones has been developed. The protocol features easy operation, excellent yields, excellent diastereo-control, broad substrate scope and good functional group tolerance.     

Hydration of C3a in the presence of CaCO3

The hydration of C₃A with and without CaCO₃ was studied. The techniques used were X-ray diffraction, thermogravimetry, differential thermogravimetry and calorimetry.In the presence of CaCO₃, the hydration of C₃A is accelerated. The hexagonal hydrates are formed first. They react with CaCO₃ to form calcium carboaluminate hydrate. This reaction blocks formation of the cubic hydrate. The latter appears when CaCO₃ is completely consumed.