Novel selenium-mediated cyclisations

The present work describes the selenium-mediated cyclofunctionalisations of alkenes. Three different areas are reported herein. Chapter 2 reports syntheses of several substrates for carbocyclisation reactions and use of selenium and Lewis acids resulting in various dihydronaphthalenes. These dihydronaphthalenes then acted as substrates for second ring forming reactions. This novel tandem double cyclisation comprises a carboannulation, a Friedel-Crafts reaction and a rearrangement. This cascade sequence has been proven to be a useful tool in the selective synthesis of dihydronaphthalenes and benzofluorenes from easily accessible stilbenes and provides fast access to polycyclic ring systems in a single step. Chapter 3 describes electrophilic selenium-mediated reactions which have been used to cyclise a range of /-keto esters to corresponding biaryl compounds under very mild conditions. The products were formed by a carboannulation via addition/elimination sequence and a subsequent rearrangement of range of alkyl and aryl groups. The key starting materials stilbene /-keto esters were readily prepared by Heck coupling and hydrolysis followed by condensation with potassium ethyl malonate. Chapter 4 describes work on catalytic selenium reagents with stoichiometric amount of hypervalent iodine to convert a range of stilbene carboxylic acids into their corresponding isocoumarins. The work also describes the selective synthesis of dihydroisocoumarins using diphenyl disulfide and dimethyl diselenide

1-Azido-N′-(phenylsulfonyl)methan­imid­amide

In the title compound, C7H7N5O2S, the aromatic ring is oriented at dihedral angles of 79.46 (2) and 89.17 (2)°, respectively, with respect to the amino­(azido)­methyl and the S(6) six-membered ring motif generated by an intra­molecular N—H⋯O inter­action [N⋯O = 2.8901 (15) Å]. Inter­molecular N—H⋯O hydrogen bonds [N⋯O = 2.9177 (15) and 2.9757 (15) Å] generate an infinite one-dimensional network along the base vector (010)

Microwave-assisted solvent free efficient synthesis of 1,3,4-oxadiazole-2(3H)-thiones and their potent in vitro urease inhibition activity

An efficient solvent free microwave assisted synthesis of 5-substituted-1,3,4-oxadiazole-2(3H)-thiones (2a-2r) from hydrazides and carbon disulfide has been accomplished in good to excellent yield. The urease inhibition activity of the resulting compounds was investigated. Preliminary bioassay indicated that the compound 2j bearing 2-bromo substituent is the most active inhibitor exhibiting IC50 12.60 ± 0.92 μM

Studies towards the synthesis of (±)-reserpine: Photocyclization mediated a novel and efficient synthesis of 11,18-dimethoxy-(20α)-18,19-didehydro-yohimban-17-one

A short, highly efficient synthesis of advanced intermediates to reserpine 1 has been developed starting from enamide 8. The enamide underwent photocyclization reaction using high pressure mercury lamp to afford the lactam 9 in excellent yield. Then lactam was reduced to the required amine 10, which upon acidic hydrolysis gave the nonconjugate ketone product 11, followed by reaction with sodium hydroxide resulted the desired conjugate ketone 12. Epoxidation, and then ring opening of the epoxide 13 with methanol yielded the desired product 14, which is key intermediate to the total synthesis of (±)-reserpine

Fast synthesis of benzofluorenes by selenium-mediated carbocyclizations

When one ring is not enough: A new double cyclization of stilbene derivatives results in benzo[b]fluorenes via dihydronaphthalenes. The presence of a selenium electrophile and a Lewis acid are crucial for the formation of the CC bonds

Selenium-Mediated Synthesis of Biaryls through Rearrangement

A new cyclization of β-keto ester substituted stilbene derivatives using selenium electrophiles in the presence of Lewis acids is described. Substituted naphthols are obtained through cyclization and subsequent 1,2-rearrangement of aryl groups under very mild reaction conditions

Diselenide- and Disulfide-Mediated Synthesis of Isocoumarins

Cyclizations of stilbenecarboxylic acids to the corresponding isocoumarin derivatives using diselenide or disulfide reagents have been developed. By employing bis(triflouroacetoxy)iodobenzene as oxidant for the 6-endo-trig cyclizations a variety of dihydroisocoumarins have been prepared in good yields. This method is capable of forming isocoumarins and dihydroisocoumarin derivatives by a cyclization–elimination route

Dimethylaluminium methylselenolate

(preparation of methyl selenoesters; aldol condensation of enones) Solubility: reaction are typically run in toluene. Preparative Methods: conveniently prepared by heating a toluene solution of Trimethylaluminum with powdered Selenium for 2 h at reflux.2 The yellow-colored supernatant was transferred to a septum-capped argon-filled Erlenmeyer flask. Handling, Storage, and Precautions: the reagent was found to retain its activity for approximately one month at rt. Selenium reagents are toxic and should be handled with caution, in a fume hood

Recent Advances in Organoselenium Chemistry

This microreview highlights new developments of organoselenium chemistry and new selenium compounds as versatile reagents in synthesis