Cyclizations potassium hexamethyldisilazide

Spirocyclic oxindole 60 was synthesized by [3,3]-sigmatropic rearrangement of the Af-phenyl-O-acylhydroxamic acid 58 (equation 19). The potassium enolate formed by treatment of 58 with potassium hexamethyldisilazide at low temperature rearranged to 59, which easily cyclized to the spirocyclic oxindole 60. Spirooxindoles were previously synthesized by Wolff and Taddei. The spirooxindole 60 was formed in 51% yield from cyclohexanecarboxylic acid after heating the preformed lithium salts of phenyl hydrazide 61 to 205-210 °C. 

The phosphorylated bromobenzamide derivative 180 cyclizes to produce the phosphorylated isoindolinone on exposure to an excess of potassium hexamethyldisilazide (KHMDS) (Equation 116) <2000T1491>. 

The group of Lai and Rafii prepared a chiral imidazolium tetrafluoroborate from commercially available (lR,2R)-l,2-diamlnocyclohexane (Scheme 2.167) [61]. Palladium-catalyzed coupling of the diamine and mesityl bromide with 3 equiv of NaOtBu produced a diamine in the first step. Cyclization of this material with triethyl orthoformate in the presence of ammonium tetrafluoroborate led to the chiral BF, salt in an almost quantitative yield [62]. Finally, the chiral rhodium complex was synthesized by reacting the ligand precursor with an equimolar amount of potassium hexamethyldisilazide, followed by coordination to rhodium with [RhCl(COD)]2. 

---