Total synthesis of (.+-.)-pentalenene, the least oxidized neutral triquinane metabolite of Streptomyces griseochromogenes

Abstract

undeca-6,9-diene (37). Methyllithium (12 mL of 1.2 M in hexane, 1.47 mmol) was added dropwise to a cold (-78 °C), magnetically stirred solution of 36 (300 mg, 1.47 mmol). The reaction was allowed to proceed for 6 h at -78 °C and then overnight at room temperature. The mixture was poured into water, neutralized with dilute hydrochloric acid, and extracted with ether. The combined organic layers were washed with brine, dried, and concentrated. The clear, colorless oil thus obtained (320 mg, 100%) was dissolved in dry benzene (20 mL) containing p-toluenesulfonic acid (50 mg, 0.26 mmol) and heated at reflux under a Dean-Stark trap. The cooled reaction mixture was washed with saturated sodium bicarbonate solution and brine prior to drying and concentration.

The economies of synthesis

“…Paquette and co-workers have developed two syntheses17 of pentalenene ( 37 ), separated by 20 years (Scheme 7). The first of these is a traditional approach proceeding in over 20 steps and involving several corrective refunctionalisations.…”

C1‐Symmetric Heterocyclic Zirconocenes as Catalysts for Propylene Polymerization, 1

“…A much higher yield than reported in the literature [32][33][34][35][36][37] was achieved by sequential addition of hydrazine and potassium hydroxide. For the coupling step 2, a nickel-catalyzed oxidative coupling method has been developed using zinc to regenerate the catalyst in situ.…”

Synthesis of (.+-.)-8-Deisopropyladunctin B

“…After selective demethylation of 28 in the usual manner, 20,21) extension of the acetyl group in 16 to the cinnamoyl group was carried out by cross-aldol condensation with benzaldehyde in the presence of t-BuOK to afford 32 in 80% yield. Finally, the double bond of the α,β-unsaturated carbonyl group of 32 was chemoselectively reduced over the isolated double bond at the 6,7-position to give (±)-8-deisopropyladunctin B (9) in 61% yield 22,23) (Chart 6). In order to confirm the structure of 9, the spectral data of 9 were compared with those of adunctin B (2) reported in ref.…”