Synthesis of Cyclopentadiene

SRPL102.
A 2000-mL threenecked
round-bottom flask fitted with a reflux condenser and a
250-mL addition funnel was charged with 16.8 g (0.443 mol) of
LiAlH4. Diethyl ether, 900 mL, was then added to the flask and
the mixture cooled to 0 °C. Freshly distilled, colorless, KSM102, 210 mL (1.40 mol), was
addeddropwise to the mixture with stirring over a 1-h period. The
mixture was allowed to warm to room temperature and stirred
for 8 h. Water, 70 mL, was then added dropwise to hydrolyze
the remaining LiAlH4. Solids were coagulated by the dropwise
addition of 70 mL of 33% H2S04, and the ether layer was decanted
into a 2000-mL separatory funnel. Water and 33% H2S04 were
added alternately to the remaining solids in the flask until all solids
dissolved. The solution was then back-extracted with Et-jO (3
X 50 mL), and the extracts were combined with the ethereal layer.
The dehydration of the alcohol was monitored via GC on a 5%
FFAP on Chromosorb W column by monitoring the disappearance
of the alcohol.14 An aliquot, 20 mL, of 33% H2S04 was added
to the ether layer in the separatory funnel and shaken for 2 min.
The aqueous layer was removed and a GC of the ether layer
recorded. This procedure was repeated with 20-mL aliquots of
33% H2S04 until no alcohol could be detected by GC. The ether
layer was then washed free of the majority of acid with water and
checked via GC for the presence of alcohol. If no alcohol was
present, a saturated aqueous solution of potassium carbonate was
added until the aqueous layer was strongly alkaline. The aqueous
layer was then removed, the combined water wash and aqueous
layer were back-extracted with 2 X 250 mL of ether, and the ether
layers were combined. Anhydrous potassium carbonate was added
to the ether layer in the separatory funnel. After 10 min, the ether
layer was then decanted onto anhydrous potassium carbonate in
a 2-L flask. Subsequent to filtration, the ether was removed by
rotary evaporation leaving a yellow to orange liquid. A small amount of sodium metal (ca. 0.3
g) was added to the flask and
the product purified by trap-to-trap distillation. Yield: 69.7 g
(45.8%).