Benz[f]indenones: A Novel Synthesis by an Anionic [4+2] Cycloaddition/Retro Diels-Alder Pathway

Synthesis of Benzo[b]fluorenone Nuclei of Stealthins

“…Initial studies were focused on the utilization of the readily accessible benz[ f ]indenones 5a and 5b [21]. DBU-promoted Michael addition of nitromethane to the indenones furnished indenones 7a and 7b, respectively.…”

“…Preparation of the key precursor 11 is depicted in Scheme 3. LDA-promoted allylation of 12 [21] with allyl bromide 13a furnished 14a. Characteristic multiplets at δ 5.6 and two doublets at δ 5.1 and δ 4.87 in 1 H NMR spectrum were in complete agreement with the structure 14a.…”

Use of Stabilized Phthalide Anion Annulation Reactions in Synthesis: An Update

“…Mal et al 5,[16][17][18][19] successfully utilized indenones and cyclopentenone as Michael acceptors in their efforts to prepare the kinamycins via phthalide annulation. They were able to produce the carbocyclic skeletons 38 and 40 of kinafluorenone (41) from 3-sulfonylphthalide (13b) and in-denones 37 and 39 (Scheme 11).…”

“…5,17 Mal et al also explored the chemistry of cyclopentenone 47, racemic indenone 42 and indenone 51 in reactions with phthalides 13b and 49 to produce polycyclic systems 43, 48, 50 and 52 (Scheme 13 and Scheme 14). 18,19 Scheme 11…”

Regiospecific Synthesis of Benzo[b]fluorenones via Ring Contraction by Benzil-Benzilic Acid Rearrangement of Benz[a]anthracene-5,6-diones

“…Initially, we attempted to extend our previously reported anionic [4+2] cyclocondensation methodology 8a,10 to the synthesis of 2,3,6,7-dibenzofluorenone 4. When dimethoxybenzindenone (3) 11 was subjected to the Hauser annulation with phenylthiophthalide (2) 10c in the presence of lithium tert-butoxide, the expected condensed product 4 was obtained in 98% yield. This was duly characterized by spectroscopic means.…”