A cyclopropabenzenylidenethenone (Propadienone) via a new route to alkylidenecycloproparenes

Reaction of 1,1-dichloro-2,5-diphenylcyclopropabenzene 6 with Meldrum's acid 8 in the presence of pyridine leads to coupling of the cycloproparenyl cation 7 with the stabilized diketo anion 9. Subsequent, spontaneous, base-induced dehydrochlorination gives the alkylidenecyclopropabenzene 11 in a one-pot reaction. Flash vacuum thermolysis of 11 at 650 degreesC ejects acetone and carbon dioxide, giving cyclopropabenzenylldenethenone 12 that is isolated in an Ar matrix at 20 K and characterized by a strong ketene band at 2107 cm(-1) in the IR spectrum.

Expedient construction of the vibsanin E core without the use of protecting groups

The tricyclic core of vibsanin E was constructed without the use of a protecting group in six steps. The El Gaied Baylis-Hillman variant was key to allowing the Bronsted acid induced tandem cyclization forming rings B and C in one operation.

Towards the total synthesis of vibsanin E, 15-O-methylcyclovibsanin B, 3-hydroxyvibsanin E, furanovibsanin A, and 3-O-methylfuranovibsanin A

Studies detailing synthetic approaches to a variety of biosynthetically related vibsanin-type diterpenes (i.e. vibsanin E, 15-O-methylcyclovibsanin B, 3-hydroxy-vibsanin E, furano-vibsanin A, and 3-O-methylfuranovibsanin A) are discussed. Biogenetically modelled approaches are coupled with an in-vestigation of classical and modern six- to seven-membered ring-expansion protocols, which gain access to the central core of these natural products. (c) Wiley-VCH Verlag GmbH & Co.