Fragmentations potassium tert-butoxide

In view of the smooth addition of carbanions to the electrophilic P atom of phosphorins (see p. 78 and 66), Markl and Merz attempted the addition of carbenoids (carbenes ) by reacting dichloromethane, trichloromethane or dichloro-phenylmethane with potassium-tert-butoxide in the presence of 2.4.6-triphenyl-X -phosphorin 22 or 2.4.6-tri-tert-butyl-X -phosphorin 24. The desired bicyclocompound 7/5 or the X -phosphepin 116 were not obtained. Instead, benzene derivatives were formed by loss of a PCI fragment, the fate of which was not determined. Markl has proposed a mechanism in which intermediates 114,115 and 116 ZK invoked ... 

Both heterobicyclic compounds 8 and 13 readily undergo a base-induced [3-1-2] cycloelimination (Scheme 3) Upon treatment with potassium tert-butoxide at room temperature, the HNCY fragment of the triazolidine moiety of 8 (Y = S) and 13 (Y = O) is eliminated, thus reversing the second step of the criss-cross cycloaddition cf. Scheme 2). 

A recent modification [la] uses potassium tert-butoxide in anhydrous dimethyl sulphoxide, when reaction is rapid even at room temperature. The enhanced rate is attributed to the high reactivity of anions in this solvent (c/. p. 45). The reaction is usually formulated as a prototropic rearrangement of the hydrazone to give a diimide (i), followed by fragmentation of the diimide anion (2) to give a nitrogen molecule and the carbanion (3) [2], Rapid protonation then affords the reduced product. A recent study [3] oi solvent effects on the reduction... 

The procedure described here represents a reliable modification of the alkylation/Thorpe-Ziegler approach to 2,2-diphenylcyclopentanone applicable to large-scale preparations. The use of LOA as the alkylation base, In exact stoichiometry, has been found to avoid over-reaction and the undesired fragmentation pathway of the enaminonitrile observed with sodium amide. The Thorpe-Ziegler cyclization proceeds smoothly employing modified literature conditions with potassium tert-butoxide as the base. Hydrolysis of the enaminonitrile with hydrochloric acid, was found to be superior to previously reported methods, which led to incomplete consumption of the intermediate cyano ketone in our hands. The ratio of solvent volume to enaminonitrile is very important and more concentrated reaction mixtures result in incomplete conversion of the cyano ketone even after prolonged heating. 

The reaction of/n-bis(3-phenylimidazo[l,5-fl]quinoxalin-4(5//)-on-l-yl)benzene 164 and the dibromide 167 (Moore et al. 1977) in the presence of potassium tert-butoxide in DMSO, or in the presence of K2CO3 in DMF gave the products 168 and 169a, b, which consisted of hemispherand (Lein and Cram 1985 Ruettimann et al. 1992) and calixarene (Vicens and Bohmer 1991) structural fragments, resulting from MA -alkylation according to the schemes [1 + 1] and [2 + 2] (Scheme 5.40) (Mamedov et al. 2014). 

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