Diaza-Cope rearrangement

Scheme 10 Diaza-Cope rearrangement of chiral 2,5-diaza-1,5-dienes and homolytic C - C bond cleavage of dimetal piperazides cause loss of stereochemical pimity...

Saczewski and Debowski reported the l,4-diaza-3-oxa-Cope rearrangement of N-cyanate anilides (equation 52). Prototropic rearomatization of 176 and internal nucleophilic addition afford the corresponding benzimidazolinone 177, usually in moderate yields (32-78%). A concerted [3,3]-sigmatropic rearrangement is proposed based on the absence of para rearrangement product that usually results from homolysis or heterolysis of the N—O bond followed by recombination of the two radicals or ions. 

In an attempt to prepare unsymmetrical bis-Schiff bases of DAMN under conditions mild enough to prevent exchange, Ohtsuka found that the unexpected, concomitant hydrolysis of the nitrile adjacent to the reaction site gave the bis-Schiff bases 131, which underwent a facile diaza Cope rearrangement giving dihydropyrazines in moderate yields, usually as mixtures of 132 and 133 (79JOC4871) (Scheme 48). 

In conclusion, mention should be made of dendronised chiral salen ligands and their Co2+ and Ni2+ complexes, which were prepared for use as Jacobsen-type catalysts by diaza-Cope rearrangement [24]. However, instead of the meso compounds produced, the enantiomers will have to be synthesised directly in enantioselective manner (Fig. 4.69). 

The N-analogs1 8 of the Cope and Claisen rearrangement have been widely used for syntheses of amines and /V-heterocyclcs, for example, the l,l -diaza-Cope rearrangement is the key step in the Fischer indole synthesis. 

Voegtie, F., Goldschmitt, E. Dynamic stereochemistry of degenerate diaza-Cope rearrangement. Angew. Chem. 1974, 86, 520-521. 

The first step of the reaction is apparently a diaza-Cope rearrangement, followed by tautomer-ization and lactam ring closure. 

In cyclic hetero-Cope rearrangements, the hypothetical diaza-semibullvaiene 14 is of considerable theoretical interest1051,1052. 

Q 17. The diamine I on heating in ethanol at ambient temperature gives II in good yield by the Diaza—Cope rearrangement. However, on heating diamine III or IV in CDCI3 at 25 °C, an equilibrium mixture is obtained that contains III and IV in a ration of 14 1. Explain the observations. 

This competing Diaza-Cope reaction needs a chair-structured geometry to produce the unwanted rearranged by-product. The key to produce these cages in a reasonable amount is to slow down the rate of the Diaza-Cope rearrangement by cooling the reaction and, for CCIO, to remove the condensation by product, such as water. ... 

Section 17-9) (2) an electrocyclic reaction (a diaza-Cope rearrangement recall Section 22-7) (3) another imine-enamine (in this case, benzenamine) tautomerization (4) ring closure to the heterocycle and (5) elimination of NH3.]... 

The effect of weak forces on the equilibrium constant for the diaza-Cope rearrangement suggests that the anion effect is the strongest followed the resonance-assisted hydrogen-bond, steric, conjugation, and electronic effects. These weak forces are said to be additive." An intramolecular Fischer indole synthesis with a double bond in the tether allows a tandem [3,3]-sigmatropic rearrangement access to tricyclic benzo[cindole systems (Scheme 1). ... 

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