Studies towards a total synthesis of kainic acid

A Cyclobutanol Ring-Expansion Approach to Oxygenated Carbazoles: Total Synthesis of Glycoborine, Carbazomycin A and Carbazomycin B

The transition-metal-free total syntheses of the oxygenated carbazole natural products glycoborine, carbazomycin A and carbazomycin B are reported. The key step involves an NBS-mediated cyclobutanol ring expansion to 4-tetralones for the preparation of the tricyclic carbazole core.

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4 , whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin.

Total synthesis of (-)-α-kainic acid via chirality transfer through Ireland-Claisen rearrangement

The total synthesis of (-)-α-Kainic acid is accomplished using a linear strategy involving Noyori asymmetric reduction and chirality transfer through Ireland-Claisen rearrangement as key steps.

Stereospecific ring expansion of chiral vinyl aziridines

In this report, it is demonstrated that chiral vinyl aziridines can be stereospecifically ring expanded. This synthetic approach allows controlled access to chiral 2,5-cis- or 2,5-trans-3-pyrroline products from starting materials with the appropriate aziridine geometry. Twenty three ring expansion examples, most of which feature a stereospecific cyclization, are presented.

Synthesis of Dihydrooxepin Models Related to the Antitumor Antibiotic MPC1001

4-Hydroxy-L-proline was converted into the tetrahydrooxepino[4,3-b]pyrrole ring system characteristic of the potent antitumor agent MPC1001. Key steps were regioselective formation of a vinylogous amide by use of Bredereck's reagent and acid-induced cyclization of an alcohol onto the carbon-carbon double bond of that amide by addition-elimination to generate the seven-membered oxacyclic subunit.

The Double Reduction of Cyclic Sulfonamides for the Synthesis of (4S-Phenylpyrrolidin-2R-yl)methanol and 2S-Methyl-4S-phenylpyrrolidine

The synthesis of (4S-phenylpyrrolidin-2R-yl)methanol and 2S-methyl-4S-phenylpyrrolidine has been achieved via the double reduction of their cyclic sulfonamide precursors which themselves were prepared following the stereoselective intramolecular Heck reaction of a chiral pool derived 2,5-dihydropyrrole. We have recently described a process whereby cyclic aryl sulfonamides, such as 2, are reductively ring-opened to furnish amino products in which the aryl group is incorporated in the final compound. (Evans, P.; McCabe, T.; Morgan, B. S.; Reau, S. Org. Lett. 2005, 7, 43.) The precursors for this reaction were assembled using an intramolecular Heck reaction followed by reduction of the alkene. Overall, this sequence represents an efficient means to construct molecules of this type in which the aryl sulfonyl moiety acts as both an N-protecting group and as an aryl donor. Use of Benkeser's stronger reducing conditions enables molecules such as 4 to be prepared in which both the sulfonamide functional group and the aromaticity of the aryl substituent have been destroyed.

Synthesis of 3'-deoxy-3'-difluoromethyl azanucleosides from trans-4-hydroxy-l-proline

[reaction: see text] Two strategies were tried to synthesize 3'-deoxy-3'-difluoromethyl azanucleosides. After the failure of the first route, the key intermediate 12 from trans-4-hydroxyproline 7 in 8 steps was stereoselectively prepared. The alcohol 12 was subjected to selective protection, oxidation, and difluoromethylenation to afford the fluorinated compound 18, whose hydrogenation was then systematically investigated. After a series of transformations of protecting groups, the resultant compounds 22 and 23 were oxidized to the desired lactams 24 and 25, which were successfully utilized to synthesize our target molecules, 3'-deoxy-3'-difluoromethyl azanucleosides 33, 34a, 34b, and 35.

Total Synthesis of (−)-(α)-Kainic Acid via a Diastereoselective Methylenecyclopropane Ring Expansion

[reaction: see text] A concise and enantioselective synthesis of (-)-(alpha)-kainic acid in 13 steps with an overall yield of 15% is reported. The pyrrolidine kainoid precursor with the required C2/C3 trans stereochemistry was prepared with excellent diastereoselectivity (>20:1) via a MgI(2)-mediated ring expansion of a tertiary methylenecyclopropyl amide. A selective hydroboration was then employed to set the remaining stereochemistry at the C4 position en route to (-)-(alpha)-kainic acid.