Spirocyclic anion

The degree of TBP — RP distortions in the spirocyclic anionic and zwitterionic germanates (Section IV.B.3) is rather similar to that observed for the corresponding silicon analogues42 for a comparable set of ligands, although as a rule the structures of Si analogues are close to the TBP. 

Multistep synthesis according to Eq. (110) affords sulfur anions 132a and 132b with unusual coordination via alcohol 131 (207). The spirocyclic anion 132b has been estimated to be 13 kJ/mol more stable than its open-chain isomer 132c. 

The distortion observed in variously substituted spirocyclic anionic methyl and phenyl germanates of substituted catachols and thiocatachols is explained... 

The only structurally characterized derivative of a trisimido organophos-phonate anion is the spirocyclic tellurium(IV) complex (19), which is obtained from the interesting redox reaction between PhPCl2 and [Li2Te(N Bu)3 ] 2 [27]. The phosphorus(V)-centered ligands are generated by imide transfer from tellurium to the phosphorus(III) atoms with concomitant reduction of one-half of the tellurium in the Te(IV) reagent to elemental tellurium [27]. 

An unusual A-chelate is the anion R MI PR2 S, which has no carbon atoms amongst the four-membered chelate ring atoms, and forms a tetrahedral bis Co11 spirocyclic complex.512 Higher denticity ligands also feature in the literature. A dipyrazoyl-dithioether ((119), bddh) forms a simple octahedral cw-a-Co(bddh)(NCS)2 complex.513 The ketal coronand (120) forms a... 

They proposed that [l,4]-sulfanyl participation gave a [2.2.1] bicyclic sulfonium salt intermediate 10a. This could be captured by the chloride anion to give either 19 (by path a) or 20 (by path b) as outlined in Scheme 3. It should be noted that the usual [l,2]-sulfanyl participation, via spirocyclic sulfonium ion 21, would only give the unrearranged chloride 19. 

An important class of borate esters is the anionic spirocyclic esters, shown in Eq. (7). The reaction of two molar equivalents of 1,2- or 1,3-diol with boric acid to form such spirocyclic esters is accompanied by dramatic decrease in pH, a consequence of the kinetic stability of these esters. This reaction... 

Spirocyclization with 2-silyt- 1,3-dithianes. Treatment of the trimcthylsilyl-alkanal 1 with fluoride ion liberates an anion that undergoes cyclization to the aldehyde group to yield 2. Various Lewis acids do not promote this cyclization. Similar desilylation of 3 is followed by an intramolecular Michael addition to give 4 in 64% yield. 

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