Diethyl-3,5-octadiene from a sulfolene

To a suspension of UDP (4.5 mmol) in toluene (10 ml) in a laboratory ultrasonic cleaning bath under N2 was added a solution of 2,2,5,5-tetraethyl-3-sulfolene (1.5 mmol) in toluene (10 ml). The sonication was continued for 30 min, during which time a bright-blue colour developed. A solution of t-BuOH in THF (0.45 mol dm-3, 4.4 mmol) was added dropwise over a period of 30 min, whereupon the potassium was completely consumed. The mixture was filtered through a short silica gel column to remove the solid precipitate, and the filtrate was concentrated under reduced pressure. Purification by HPLC (Lichrosorb column, hexane) yielded the corresponding diene in a 92% yield. 

Takayama et al. [547] have shown that 3-sulfolene can be directly alkylated at the 2 and 5 positions. The 2-substituted 3-sulfolenes (4) were obtained in a fair yield when the labile sulfolene a-carbanion was generated by LHMDS in a THF-HMPA solution at -78°C in the presence of an alkyl iodide. /ra/is-2,5-Dialkyl-3-sulfolenes (5) were similarly 

Interestingly, from these /ram-2.5-disubstituted-3-sulfolenes (5), desulfonylation conditions [547] yielding stereoselectivity either (E,Z) or (E,E) conjugated dienes were found and applied to stereoselective syntheses of insect pheromones (including (2)). 

The observed stereospecificity of the reductive desulfonylation of (5) by LiAlH, m refluxing ether is also of particular interest. 

The direct alkylation of 3-sulfolene followed by thermal extrusion of sulfur dioxide led [548] to a convenient synthesis of ( )-l,3-butadienyl(tributyl)stannane. 

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