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3.8.2 Synthesis of Cyclobutenes through Electrocyclization of Dienes

DOI: 10.1055/sos-SD-203-00232

Gaspar, B.; Trauner, D.Science of Synthesis: Stereoselective Synthesis, (20113385.

Electrocyclic ring opening reactions are reversible, which means that the synthesis of cyclobutenes is feasible via electrocyclic ring closure of dienes. However, the thermodynamic equilibrium for most cyclobutenes favors the open-chain diene derivative. Nevertheless, this equilibrium can be shifted toward the cyclic product by appropriate substitution. For example, some vinylallenes have been reported to undergo unidirectional electrocyclization to alkylidenecyclobutenes.[‌12‌] In this context, the combination of vinylallenes with a silyl or boryl substituent has proved particularly fruitful (Scheme 4). For example, the ring closure of vinylsilane 11 proceeds smoothly at about 145°C to afford the trimethylsilyl-substituted cyclobutene 12 in 95% yield.[‌13‌] Similarly, the boryl-substituted vinylallene 13 undergoes cyclization to furnish 14, which provides an unusual intermediate thanks to the doubly allylic boron group.[‌14‌]

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