Several biologically active natural products have a structure with vicinally dialkylated five-membered carbocycles: prostaqlandins, 1 pyrethroids,2 brefeldin A,3 jasmonoids,4 and so on. Cyclopentadiene is the most simple and reactive five membered carbocyclic compound and is considered to be suitable as a starting material for them, but the selective method to introduce two alkyl chains into the vicinal position of the diene has not been studied much.
Generally, alkylation of monosubstituted cyclopentadiene has a poor reqioselectivity, 5 since the location of double bonds is not fixed in a cyclopentadiene ring. 6 Recently, the reqiospecific method by the intramolecular steric control using a carbonate ester of cyclopentadienylethanols has been reported from our laboratory' to give cyclopentadienolactones.
In the course of the study, the double bonds were found to be fixed in the cyclopentadiene ring when an acyl group is introduced on the ring. For example, the double bonds in cyclopentadienolactone(1) place to have the direction of the longest conjugation with the carbonyl group. By the use of this system, the second substituent would be introduced reqioselectively.
We now report here a novel method for the selective synthesis of 2-acyl-6-aminofulvenes from cyclopentadiene by one-pot procedure using a method by a resonance control of acylcyclopentadienes.