Stereoselective Lewis Acid Mediated (3+2) Cycloadditions of N‐H‐ and N‐Sulfonylaziridines with Heterocumulenes

Alkyl and aryl isothiocyanates and carbodiimides are effective substrates in (3+2) cycloadditions with N‐sulfonyl‐2‐substituted aziridines and 2‐phenylaziridine for the synthesis of iminothiazolidines and iminoimidazolidines. Additionally, the stereoselective (3+2) cycloaddition of N‐H‐ and N‐sulfonylaziridines with isothiocyanates can be accomplished, allowing for the synthesis of highly enantioenriched iminothiazolidines. Evidence for an intimate ion‐pair mechanism is presented herein in the context of these chemo‐, regio‐, and diastereoselective transformations. The demonstrated ability to remove the sulfonyl group from the heterocyclic products displays the utility of these compounds for further derivatization and application.     

From Disilene (SiSi) to Phosphasilene (SiP) and Phosphacumulene (PCN)

The generation of heavier double‐bond systems without by‐ or side‐product formation is of considerable importance for their application in synthesis. Peripheral functional groups in such alkene homologues are promising in this regard owing to their inherent mobility. Depending on the steric demand of the N‐alkyl substituent R, the reaction of disilenide Ar₂Si?Si(Ar)Li (Ar=2,4,6‐iPr₃C₆H₂) with ClP(NR₂)₂ either affords the phosphinodisilene Ar₂Si?Si(Ar)P(NR₂)₂ (for R=iPr) or P‐amino functionalized phosphasilenes Ar₂(R₂N)Si? Si(Ar)?P(NR₂) (for R=Et, Me) by 1,3‐migration of one of the amino groups. In case of R=Me, upon addition of one equivalent of tert‐butylisonitrile a second amino group shift occurs to yield the 1‐aza‐3‐phosphaallene Ar₂(R₂N)Si? Si(NR₂)(Ar)? P?C?NtBu with pronounced ylidic character. All new compounds were fully characterized by multinuclear NMR spectroscopy as well as single‐crystal X‐ray diffraction and DFT calculations in selected cases.     

The Simplest,Isolable, Alkynyl Isocyanate HC≡CNCO: Synthesis and Characterization

Alkynyl isocyanates have been postulated as highly reactive intermediates in synthetic chemistry. Herein, the parent molecule HC≡CNCO is isolated for the first time. In sharp contrast to the previously reported short lifetime (ca. 15 s) at room temperature, we found that HC≡CNCO has a lifetime of 55 h in the gas phase (2 mbar, 300 K) with a melting point of ?79.5 °C and vaporization enthalpy (ΔH_vap) of 23.1(1) kJ mol^?1. Apart from the IR (gas, solid, and matrix), ¹H and ¹³C NMR, and UV/Vis spectroscopic characterization, its photoisomerization with a acylnitrene HC≡CC(O)N and cyanoketene NCC(H)CO has been observed.     

Synthesis of substituted 2-amino-5,6-dihydropyrimidin-4-ones using an aza-Wittig reaction

An aza-Wittig reaction has been used for the first time in the synthesis of substituted 2-amino-5,6-dihydropyrimidin-4-ones via condensation of triphenyliminophosphoranes with aromatic heterocumulenes (arylisocyanates and thiocyanates). __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 1037–1041, July, 2006.     

N‐Alkylsulfonylimines as Dipolarophiles in Cycloaddition Reactions

First described in the late 1960s, N‐alkylsulfonylimines are heterocumulenes that participate in reactions with a range of 1,3‐dipoles to afford interesting 3‐, 4‐, 5‐, and 6‐membered heterocycles. The distribution of adducts obtained suggests that multistage, stepwise mechanistic pathways rather than a concerted process are in operation.     

Synthesis of 4,5-dihydrothiazole derivatives by the reaction of perfluoro-2-methylpent-2-en-3-yl isothiocyanate with ambident N,O- and N,S-nucleophiles

The reactions of perfluoro-2-methylpent-2-en-3-yl isothiocyanate with ambident N,O- and N,S-nucleophiles (thiazole-2-thione, pyridine-2-thione, 2-hydroxypyridine, benzothiazole-2-thione, benzoxazole-2-thione, 3,4,5,6-tetrahydropyrimidine-2-thione) in the presence of triethylamine yield only 2-N-substituted 4,5-dihydrothiazole derivatives. The molecular structures of three products were determined by X-ray diffraction analysis. The reaction pathways are discussed.