Spiro compound

[2]: SP-0 [3]: 653, 839  The presence of only one common atom connecting the two rings distinguishes spiro compounds from other bicyclics.

[4][3]: 653ff  : 839ff  Spiro compounds may be fully carbocyclic (all carbon) or heterocyclic (having one or more non-carbon atom).

One common type of spiro compound encountered in educational settings is a heterocyclic one— the acetal formed by reaction of a diol with a cyclic ketone.

[6] The spirocyclic core is usually prepared by dialkylation of an activated carbon center.

Cases with a spiro heteroatom such as boron, silicon, and nitrogen (but also other Group IVA [14] are often trivial to prepare.

[14] Likewise, a tetravalent neutral silicon and quaternary nitrogen atom (ammonium cation) can be the spiro center.

[5]: 1139f Particularly common spiro compounds are ketal (acetal) formed by condensation of cyclic ketones and diols and dithiols.

[5]: 1138ff, 1119ff [3]: 319f.846f  Hence, in the third case, the lack of planarity described above gives rise to what is termed axial chirality in otherwise identical isomeric pair of spiro compounds, because they differ only in the right- versus left-handed "twist" of structurally identical rings (as seen in allenes, sterically hindered biaryls, and alkylidenecycloalkanes as well).

[clarification needed] Nomenclature for spiro compounds was first discussed by Adolf von Baeyer in 1900.

Structure of C 17 H 20 , which contains seven spiro atoms and eight cyclopropane rings [ 1 ]
Synthesis route to Fecht's ester, illustrating a dialkylation route to a spiroheptane .
Synthesis route to spiroundecane. [ 8 ]
The synthesis of a spiro-keto compound form a symmetrical diol
The synthesis of a spiro-keto compound form a symmetrical diol
Preparation of a spiro ketal. [ 13 ]
Two enantiomers of a spiro diketone.