The simplest spiro-connected diene, it is very unstable—decomposing even below −100 °C—due to its high bond strain and does not occur in nature.

[1][2] Spiropentadiene was synthesised from bistrimethylsilylpropynone 1 by reaction with p-toluenesulfonylhydrazide to tosylhydrazone 2 followed by treatment with sodium cyanoborohydride to allene 3 and followed by two successive reactions with chlorocarbene generated from methyllithium and dichloromethane to spiro compound 5.

[3] An all-silicon derivative (Si5 frame, (tBuMe2Si)3Si side groups) is also known.

[4] In contrast to the carbon parent this compound is stable with a melting point of 216 to 218 °C.

The angle between the two rings as measured by X-ray single-crystal analysis is 78°.