An efficient catalytic method for fulvene synthesis

Abstract

The effects of the nature and amount of base, substrate structure, amount of added water and solvent on the condensation of carbonyl compounds with cyclopentadiene in the presence of secondary amines were investigated. Based on these studies, a new efficient and green synthesis of fulvenes was developed.

Preparation of a Key Tetraene Precursor for the Synthesis of Long Acenes

“…was obtained as a yellow oil and used in next step without any further purification. 1 H NMR and 13 C NMR were in agreement with the published data for 2 prepared at the 5 mmol scale , …”

Pyrrolidine catalyzed reactions of cyclopentadiene with α,β-unsaturated carbonyl compounds: 1,2- versus 1,4-additions

“…Whereas we observed exclusive 1,2-addition to cinnamaldehyde with either stoichiometric (Little conditions, MeOH) or catalytic pyrrolidine (10 mol% in MeOH/H 2 O, 4:1, Coskun, Erden) 9 leading to a 6-vinylfulvene, Hayashi et al reported exclusive Michael attack with chiral diphenylprolinol TBS ether (10 mol%) and with or without p -nitrophenol (20%) as an additive (Scheme 2). 10 They attributed the achieved asymmetric induction and exclusive 1,4-attack to an unprecedented “ene” reaction of cyclopentadiene and postulated a cyclic transition state for a concerted proton transfer from cyclopentadiene to the α-carbon of the iminium ion and concomitant attack of the developing cyclopentadienyl anion at the β-carbon of cinnamaldehyde.…”

“…Also, in view of the surprising report by Hayashi postulating a novel ene reaction of cyclopentadiene with cinnamaldehyde resulting in a Michael addition, we studied the reactions of 1 with benzalacetones under our conditions (method C in ref. 9), using 10% pyrrolidine in MeOH/H 2 0 (4:1). The results from these reactions are shown in Table 2.…”

“…3 Benzalacetone 13 was obtained commercially. Though the other benzalacetones in Table 2 (entries 2-7) are all known compounds, we found that they are most conveniently prepared by the catalytic method we use for our fulvene synthesis 9 (MeOH/H 2 O 4:1, 10% pyrrolidine, see below).…”

Reaction of Arylnitroso Derivatives: Synthesis of Arylimino 2,5-Dihydrofuran and Arylamino Fulvenes Derivatives

“…These structures are subunit of several bioactive natural and synthetic products [14] [15]. Fulvenes have high relevance as synthons [16] [17] and materials [18]- [24]. This report will provide a fast and easy protocol to execute the preparation of the abovementioned heterocycles cores.…”