Previously we have shown that palladium catalysts effect the decarboxylation of vinyl oxazinones to form zwitterionic π-allyl palladium intermediates (A, Scheme 1).1 Thus, vinyl oxazinones can be equated with zwitterionic synthons (B). In the absence of other electrophiles, the zwitterionic intermediate cyclizes to form vinyl azetidines with high diastereoselectivity. Moreover, in the presence ...

The scope of applications of dialkyl dicyanofumarates and maleates as highly functionalized electron-deficient dipolarophiles, dienophiles and Michael acceptors is summarized. The importance for the studies on reaction mechanisms of cycloadditions is demonstrated. Multistep reactions with 1,2-diamines and β-aminoalcohols leading to diverse five- and six-membered heterocycles are discussed. Appl...

Camphor-derived oxazoline-N-oxides are versatile dipoles in a new kind of asymmetric [2+3] cycloadditions. Recent applications of this methodology allowed the stereoselective syntheses of several β-lactones natural products such as 1233A and tetrahydrolipstatine. Two formal syntheses of β-lactams antibiotics, β-methyl thienamycin and carpetimycin A, have also been achieved using this type of cy...

Indoles substituted by electron-depleted thio groups at positions 1 and 3 react as C2 = C3 dipolarophiles with an electron-rich azomethine ylide dipole under flow conditions. The dearomatizing (3 + 2) cycloadditions readily occur to afford the corresponding fluorinated 3D-pyrrolidinoindolines bearing a tetrasusbtituted carbon centre ring junction.

The synthesis of new indoloannulated thiopyranethiones is reported. key-step a rhodium-catalyzed [2 + 2 2]-cycloaddition alkynyl-ynamides with carbon disulfide to close the pyrrole and thiopyranethione rings simultaneously. A violet idolothiopyrane thione or mixture red isomer result from [RhCl(C8H14)2]2/3BINAP catalyzed cycloadditions, regiochemistry controlled by substitution pattern on alkyn...

A new condensed form of the Fukui function, the natural orbital Fukui function (NOFF), is proposed and derived from natural bond orbital occupancy. It is defined as the change in natural bond orbital occupancy upon electronic perturbation (electron addition to, or depletion from, a molecular system). Applying NOFF to a series of cycloaddition reactions (e.g., [4 + 2] and [2 + 1] cycloadditions)...

Before any of the eleven possible quinones of azulene were known, predictions were made about their proper— ties on the basis of Hickel, MINDO/3, PPP and ab initio SCF (STO—3G) calculations (3). Four unsubstituted quinones of azulene have now been prepared, and the experimental results obtained so far provide information regarding their stability, reduction potentials, cycloadditions with cyclo...

The coupling of proline- and azetidinone-substituted alkenes to 2-azidobenzoic and 2-azidobenzenesulfonic acid gives precursors that undergo intramolecular azide to alkene 1,3-dipolar cycloadditions to give imine-, triazoline- or aziridine-containing pyrrolo[1,4]benzodiazepines (PBDs), pyrrolo[1,2,5]benzothiadiazepines (PBTDs), and azetidino[1,4]benzodiazepines. The imines and aziridines are fo...

A simple methodology for encapsulating ca. 10 nm-sized superparamagnetic Fe3O4 nanoparticles in zeolitic imidazolate frameworks (ZIF-8) crystals was developed. The corresponding Fe3O4@ZIF-8 heterostructured material exhibits bifunctional properties with both high magnetization (Fe3O4) and high thermal stability, large specific surface, and catalytic properties (ZIF-8). The Fe3O4@ZIF-8 catalyst ...

The idea of similarity index was extended to the investigation of the effect of spin recoupling in chemical reactions. The approach was applied at the semiempirical AM1 level to a series of selected pericyclic reactions involving model examples of electrocyclic reactions, cycloadditions and valence isomerizations. Both allowed and forbidden reaction mechanisms were analyzed in each case with th...