Zum Mechanismus der Cyclopropan‐“Walk”‐Umlagerung: Synthese und Eigenschaften eines optisch aktiven Diazoalkan‐Addukts von Toluol; eine hochstereoselektive N₂‐Eliminierung

Abstract

The synthesis and the thermal and photochemical behavior of the optically active 2-diazo-1-methoxypropane-toluene adduct 3 are reported. The Nz elimination of 3 ocurs with one and the 1. Synthese des optisch aktiven 2-Diazo-1-methoxypropan-Toluol-Addukts 3Da Benzol und seine Alkyl-substituierten Derivate mit Diazoalkanen nicht im Sinne einer 1,3-dipolaren Cycloaddition reagieren, wahlten wir analog zur Synthese des 2-1 2 Y Y 3 4 X, Y = CH,, CH20CH, Diazopropan-Toluol-Addukts den Dihydrobenzoesaureester 54) als Ausgangsverbindung. Die Reaktion von 5 mit 2-Diazo-l-methoxypropan5) (6) bei 0°C ergab die beiden diastereomeren 1,3-dipolaren Cycloaddukte 7a und 7 b im Verhaltnis 3 : 1, die sich chromatographisch trennen lieBen. Chem. Ber. 1992, 125, 197-208 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1992 0009 -2940/92/(b101-0197 S 3.50+.25/0 3.' 10'' a: EtzO, 0°C: 15% 7a, 5% 7b.b: 96% 8a (R = CH20H), 87% 8b (R TsC1. 25°C: 55% 8 a (R = CH,OTs) 1) DIBAL-H, Et20, -78°C: ,, 52% 8b (R = CH~OTS); 3) = CH,OH); 2) NaH, Et20, LiEtiBH, THF, O°C:'66% 8a=(R = CH3)=8a, 55% 8b (R = CH3) = 8b.c: 8 a + Brom auf polymerem Trager (Amberlyst A-23 Br3; Fluka), CH2CIz, 25°C: 91% 9a.d: KOtBu, THF, 0°C: 35% 3.e: 1) 8b + Brom auf polymerem Trager, CH2C12, 25°C: 88%; 2) KOtBu, THF, 0°C: 60% 10.

Epimerization of Cyclic Vinylphosphirane Complexes: The Intermediacy of Biradicals

“…In these cases the mechanistic pathway is considered to involve a biradical intermediate. An elegant illustration of a biradical process is the thermally or photochemically induced “walk” or circumambulatory rearrangement of bicyclo[4.1.0]hepta-2,4-diene which occurs though mainly with inversion of the apical cyclopropane carbon (eq 5) . Using an optically active diazo precursor to generate the biradical intermediate, Klärner showed that its ring closure occurs faster than the rotation of the single bond.…”

Tether-directed remote functionalization of fullerenes C60 and C70

“…Thermal and photochemical extrusion of dinitrogen from pyrazolofullerene 10, affording homofullerene (±)-11 and a mixture of the latter and methanofullerene 12, respectively. of N 2 -elimination from diazoalkane-toluene adducts [32] as well as high-level calculations [33], thermolysis was proposed to pass through a Möbius aromatic transition state in an eight-electron orbital-symmetry-controlled [2π s + 2π s + 2σ s + 2σ a ] process [31,33]. It leads to an intermediate norcaradiene substructure that cycloreverts to the cycloheptatriene unit of homofullerene derivative (±)-11.…”