Dipakranjan Mal

Phthalides and Phthalans: Synthetic Methodologies and Their Applications in the Total Synthesis

1. Phthalides A 1.

Benzannulation for the regiodefined synthesis of 2-alkyl/aryl-1-naphthols: total synthesis of arnottin I.

The annulation of phthalides with α-alkyl/arylacrylates in the presence of LDA/LHMDS is shown to directly give alkyl/aryl-1-naphthols. The method involving a novel dealkoxycarbonylation obviates the regiochemical issues in the synthesis of polysubstituted naphthalenes, and it forms the key step in a three-step total synthesis of arnottin I, a naphthobenzopyranone natural product.

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.

Total synthesis of euplectin, a natural product with a chromone fused indenone.

The first total synthesis of euplectin, a rare metabolite with a chromone annulated indenone motif, has been accomplished in 17 steps. This has been possible through interplay among three key reactions: a Hauser sulfoxide annulation, a new chromone formation and a late-stage retro-Diels-Alder reaction. The entire regiochemical integrity of the successful route is established by an iodine-catalyzed aromatization of a cyclohexane-1,3-dione and the Hauser annulation.

Mo(CO)6-promoted facile deoxygenation of α,β-epoxy ketones and α,β-epoxy esters

Abstract Deoxygenation of α,β-epoxy ketones and α,β-epoxy esters is accomplished in high yields under mild and neutral conditions by the use of Mo(CO) 6 .

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 ).

DBU-CH3I, a Potential Substitute for CH2N2 in the Preparation of Methyl Esters and Methyl Aryl Ethers : Studies with Assorted Acids

Abstract DBU-CH3I has been poised to be a substitute for diazomethane in the preparation of methyl esters from carboxylic acids. The reactions can be carried out in commercial untreated acetone and acetonitrile, which have been exemplified with several methyl esters, otherwise it is difficult to prepare. Bis-esterification using diiodomethane can also be achieved in a similar fashion. Sufficiently acidic phenols are also conveniently O-methylated by the method.

Anionic [4+3] heteroannulation of 2-azidoacrylates: a modular synthesis of 2-benzazepin-1-ones

2-Azidoacrylates undergo [4+3] annulation with phthalides under anionic conditions at low temperatures to furnish 5-hydroxy-2-benzazepinones, the formation of which represents a new concept for the construction of azepines as well as a new reactivity of 2-azidoacrylates.

Synthesis of Vitamin K and Related Naphthoquinones via Demethoxycarbonylative Annulations and a Retro-Wittig Rearrangement

Anionic annulations of 3-nucleofugal phthalides with α-alkyl(aryl)acrylates involving a demethoxycarbonylation provide a succinct synthesis of vitamin K and related naphthoquinones. Also reported is a new cascade reaction stemming from a Cope-retro-Wittig rearrangement. This cascade leads to direct formation of 1-hydroxy-4-prenyloxynaphthalene-2-carboxylates from the corresponding α-prenyl acrylate acceptors.

A sequential anionic [4 + 2] cycloaddition and thermal [4 + 2] cycloreversion strategy to furocoumarins : A concise synthesis of methoxsalen

Abstract The synthesis and utility of unprecedented fluorenofurans 7 and oxa- s -indacenones 8 as key intermediates for synthesis of methoxsalen 1 is described, illustrating a novel synthetic approach to furocoumarins.