Sujit K. Ghorai

Total synthesis of coriandrin and 7-demethylcoriandrin via a new synthesis of isocoumarins

Abstract Indenone epoxides 8 , prepared from the corresponding indenones, have been shown to undergo clean thermal rearrangement to give isocoumarins 10 in high yields. This synthesis of isocoumarins, when applied to oxaindacenone 7 , resulted in the total synthesis of coriandrin ( 1 ).

Synthesis and rearrangement of quinone-embedded epoxycyclopentenones: a new avenue to pyranonaphthoquinones and indenopyranones.

The epoxyquinones (e.g., 24), readily assembled in one step from the quinols (e.g., 27) by a simplified version of the Dowd oxidation, are shown to undergo rearrangement to pyranonaphthoquinones (e.g., 28) and their ring contracted homologues (e.g., 29) on flash vacuum pyrolysis at 450 degrees C and 0.01 Torr. The rearrangement has been demonstrated to be useful for a regiospecific synthesis of lambertellin (3). Similarly, the masked aziridinocyclopentanone 9 rearranges to 2-pyridone (37).

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.

A SIMPLE AND EFFICIENT METHOD FOR THE EPOXIDATION OF α, β-UNSATURATED ALDEHYDES AND KETONES USING AQUEOUS HYDROGEN PEROXIDE-SODIUM ETHOXIDE

Epoxidation of carbon-carbon double bonds conjugated to caxbonyl groups is a process of great synthetic utility.’ There exist in the literature a large number of procedures* for the preparation of epoxides from the corresponding a,&unsaturated carbonyl compounds. Most commonly, aqueous hydrogen peroxide in combination with inorganic bases (e.g., NaOH, LiOH3a, N%C0,3b, hydrotalcite”, etc.) is utilized. terr-Butyl hydroperoxide in the presence of different bases (Bu,F, KF-Al,O,, NaOH, Triton B, KH, KO‘Bu, BuLi, etc.)* is also employed. Alternatively, anhydrous tert-butyl hydr~peroxide~ in the presence of an organic base, namely, DBU and cyclic guanidines’ is recommended for the transformation where use of hydrogen peroxide fails. Occasionally, sodium hypochlorite6 in the presence of hexamethylguanidinium chloride has also been used for such purposes. In recent years, development of H,O,-based heterogeneous catalytic systems7 has been an active area of research. While the existing methods serve well the need of synthetic organic chemistry, the yields of the reactions vary widely for different substrates and on many occasions they are abysmally low for multi-step reaction sequences. The work of Wipf et aL8 on the epoxidation of naphthoquinone spiroketals clearly demonstrates that the existing methods based on hydrogen peroxide may lead to decomposition of products and there is a need for further development in this area. Recently, we reported a total synthesis’ of coriandrin (3) by a new route in which one of the key steps was a thermal rearrangement of epoxide 2 to isocoumarin 3. Though the synthesis was concise, it was plagued by low yields of the epoxide 2.

1,4-Methano-11a-methyl-4,4a,11,11a-tetrahydro-1H-benzo[b]fluoren-11-one.

The title compound, C(19)H(16)O, crystallizes with two molecules of opposite chirality in the asymmetric unit. In both molecules, the naphthalene and cyclopentanone moieties are individually planar. The two cyclopentane rings adopt envelope conformations, while the cyclohexane ring adopts a boat conformation.

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.

3-(Phenylthio)phthalide: an Expedient Reagent in Phthalide Annulation

3-(Phenylthio)phthalide 4 is more readily accessible than the established reagents 1 and 2 and can be engaged in phthalide annulation with comparable efficacy.

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.