Nirmal Kumar Hazra

A rapid access to hydroxylated benz[a]anthraquinones: Hypervalent iodine oxidation of β-naphthols

Abstract Anionic annulation of phthalide sulfones 3 with quinone monoketals 6 , accessible by phenyliodonium diacetate oxidation of naphthols 5 , offers a high yielding regiospecific entry to benz[ a ]anthraquinones 8 . Similar annulation of cyanophthalide 13 with 12 , followed by photooxygenation of 14 results in a complementary route to the basic skeleton 15 of nonaromatic A - ring angucyclines.

The first approach to kinamycin antibiotics: Synthesis of kinafluorenone scaffold

Abstract Annulation of indenone 5 with phthalide sulfone 6 has been successfully performed to furnish model benzo [b] fluorenone 7 , illustrating a potential route to kinamycin antibiotics.

Facile synthesis of 4-functionalized cyclopentenones

Abstract 1-8-Diazabicyclo[5.4.0]undec-7-ene(DBU)‐catalyzed Michael addition of nitroalkanes to dicyclopentadienone (1) followed by flash vacuum pyrolysis (FVP) provided a high‐yielding synthesis of extremely pure 4‐nitroalkyl cyclopentenones (3). The optimized Nef reaction of the nitro adducts (2) provided 4‐ketoalkyl cyclopentenones (5) in the similar way.

A convenient synthesis of benz[f]indene

Abstract The crucial annulation of sulfone aldehyde 2 with enone 3 has led to an operationally simple two-step synthesis of benz[ f ]indene 1 , and its derivatives 8 and 9 involving a new rearrangement.

Tandem Cope–cheletropic reaction: a new molecular rearrangement

The pentacyclic naphthoquinones 8 undergo unprecedented thermal rearrangement to cyclopent[a]anthraquinones 7 or 9 via a tandem Cope–cheletropic reaction path.

Synthesis of Benzo[]fluorenone Nuclei of Stealthins

Two routes, one based on a Michael-initiated aldol condensation and the other on an intramoleculer carbonyl-ene reaction, have been found to be feasible for an entry to benzo[𝑏]fluorenones. Reaction of 4,9-dimethoxybenz[𝑓]indenone with nitromethane in the presence of DBU gave the corresponding Michael adduct, which afforded 2-methyl-5,10-dimethoxybenzo[b]fluorenone on reaction with methacrolein under a variety of basic conditions. Similarly, 2-methallyl-4,9-dimethoxybenz[𝑓]indenone reacted with nitromethane to give the corresponding Michael adduct, Nef reaction of which furnished 3-formyl-2-methyl-4,9-dimethoxybenz[𝑓]indanone. This underwent ene-cyclization under the influence of SnCl4. 5H2O, and yielded 2-methyl-5,10-dimethoxybenzo[𝑏]fluorenone.

6,11-Dihydroxy-1,4-methano-1,4,4a,12a-tetrahydronaphthacene-5,12-dione

The title compound, C 19 H 14 O 4 , exists in the quinol form. The six-membered and five-membered rings of the norbornene moiety adopt boat and envelope conformations, respectively. The hydroxyl groups are involved in O-H…O intramolecular hydrogen bonds.

5,10-Dimethoxy-1,4-methano-1,4,4a,11a-tetrahydrobenzo[b]fluoren-11-one oxime

In the title compound, C 20 H 19 NO 3 , the oxime moiety C=N-O-H adopts a trans conformation. Furthermore, the molecule as a whole exists in a dimeric form through hydrogen bonding between the oxime groups.

4,4a,4b,5,6,7,9,9a-Octahydro-1,4-methano-7-methyl-5-nitro-1H-fluoren-9-one

In the title compound, C 15 H 17 NO 3 , the six-membered ring adopts an envelope conformation and the nitro and methyl groups are attached in equatorial and bi-axial positions, respectively. In the norbornene ring system, the six-membered ring adopts a boat conformation and the two five-membered rings formed by the bridging C atom adopt envelope conformations. The fused five-membered ring is in a conformation intermediate between a flattened envelope and a half-chair. In the solid state, the C=O group is involved in weak C-H…O hydrogen bonds.

1,9a‐Epoxy‐1,2,3,4,4a,4b,5,8,8a,9a‐decahydro‐2‐methyl‐4‐nitro‐5,8‐methano‐9H‐fluoren‐9‐one

The six-membered ring of the title compound, C 15 H 17 NO 4 , adopts a half-chair conformation, and the methyl and nitro groups are attached equatorially to it. The five-membered ring fused to it is in a flattened envelope conformation. In the norbornene ring system, the six-membered ring adopts a fairly symmetrical boat conformation and the two five-membered rings formed by the bridging C atom adopt envelope conformations. The mean plane through the fused five-membered ring forms dihedral angles of 31.14(5) and 84.28 (7)° with the mean planes of the adjacent six-membered rings.