Barry B. Snider

Synthesis of the tricyclic portions of batzelladines A, B and D. Revision of the stereochemistry of batzelladines A and D

Abstract The tricyclic portion 4 of batzelladine B ( 2 ) is obtained from 10a , which differs in one side chain from the ptilomycalin A model 10c that we prepared several years ago, by reduction with NaBH 3 CN in buffered MeOH. Hydrogenation of 11b over Rh Al 2 O 3 at 50 PSI H 2 affords the proposed tricyclic portion 12b of batzelladine A ( 1 ). Epimerization of 12b and hydrolysis affords acid 3 , which is similar to, but different from, the acid obtained from hydrolysis of 1 . A five step sequence converts 7b to the anti tricyclic acid 15 , which is identical to the hydrolysis product of 1 . The stereochemistry of the hydrolysis product 15 was confirmed by NOE experiments.

Synthesis and homopolymerization studies of vinylimidazolium salts

Abstract The preparations and characterizations of several monomeric vinylimidazolium salts are presented from the quaternizations of 1-vinylimidazole and 2-methyl-1-vinylimidazole with n-alkyl iodides and with dimethyl sulphate. Although vinylimidazolium salts have been reported in the patent literature, many of these salts were not isolated and characterized prior to their polymerization. From the reactions of 1-vinylimidazole with n-alkyl iodides, a homologous series of 3-n-alkyl-1-vinylimidazolium iodides were prepared in which the longer chain derivatives appeared to form micelles in aqueous solution. Dicationic crosslinking agents were also prepared through similar quaternization reactions. All the cationic vinyl monomers were homopolymerized in aqueous solution by free radical initiation. The solution behaviour of the resulting polyions indicated that the longer side-chain polyions had polysoap properties.

A Synthetic Precursor of Verrucarin A

The trichothecane antibiotics, produced by the fungi Trichothecium, Trichoderma, Myrothecium and Fusarium constitute an important class of antifungal, cytotoxic and phytotoxic sesquiterpenes. These compounds are all oxygenated derivatives of the tetracyclic 12,13-epoxytrichothec-9-ene (1) skeleton. Verrucarin A (2), a potent cytotoxin with significant anti-tumor activity, gives the trichothecane verrucarol on hydrolysis. In addition to verrucarin A, several other macrolides also contain a verrucarol moiety.

Synthesis of the tricyclic triamine core of martinelline and martinellic acid

Abstract The tricyclic triamine core27 of martinellic acid (2) has been prepared stereospecifically in eight steps from 2-hydroxymethylaniline in 11% overall yield. The key steps are the addition of 2-hydroxymethylaniline to vinylcyclopropane14 to prepare cycloaddition precursor19 in only two steps and an intramolecular [3+2] azomethine ylide cycloaddition reaction to produce tetracycle20 with>9:1 diastereoselectivity. Download : Download full-size image

Alkylaluminum halides : Lewis acid catalysts which are brønsted bases

Abstract Alkylaluminum halides react with Bronsted acids to liberate an alkane and generate a new Lewis acid. Using these reagents, Lewis acid catalyzed reactions can be run under aprotic conditions, even when acidic protons are produced in the reaction. The use of these reagents for Lewis acid catalyzed ene, Diels-Alder and cycloaddition reactions and Claisen rearrangements is described. These reagents are also useful initiators for cation-olefin addition reactions. In some cases the alkyl groups react as nucleophiles. While this is often undesirable, addition of an alkyl group to carbenium ion intermediates provides novel classes of compounds.

Synthesis of (−)-Berkelic Acid

An extremophilic challenge: Stereospecific condensation of a fully functionalized ketal aldehyde and a 2,6-dihydroxybenzoic acid is the key step in the synthesis of (-)-berkelic acid confirming Fürstners reassignment of the stereochemistry at C18 and C19, establishing the absolute stereochemistry, and tentatively assigning the stereochemistry at C22.

An Improved Procedure for the Conversion of Alkenes and Glycals to 1,2-Diazides Using Mn(OAc)3·2H2O in Acetonitrile Containing Trifluoroacetic Acid

Abstract Alkenes and Glycals react with Mn(OAc3)·2H2O and NaN3 in 9:1 acetonitrile-trifluoroacetic acid to give 1,2-diazides in >80% yield. Allylic azides are formed by slow addition of NaN3 to a mixture of alkene, Mn(OAc)3·2H2O and Cu(OAc)2.

Manganese (III) based oxidative free-radical cyclizations. 2. Polycyclization reactions proceeding through tertiary cations.

Abstract Oxidative cyclization of 5 with Mn(OAc) 3 ·2H 2 O gives mainly the bicyclic products 7 and 8 . On the other hand, oxidative cyclization of 16 and 17 gives mainly the lactones 18 and 20 . These data suggest that oxidation of a monocyclic radical to a cation precedes cyclization to form 3 , 4 , 7 , and 8 .

Synthesis of the hindered N,N,N′-trisubstituted guanidine moiety of martinelline and martinellic acid

Abstract Hindered guanidines can be prepared by reaction of cyanamides with amines in hexafluoroisopropanol at 90–120°C. This sequence was used for preparing guanidinium acid 21 as a model for martinellic acid.

Manganese (III) based oxidative free-radical cyclizations. 3. Polycyclization reactions proceeding through secondary radicals.

Abstract Oxidative cyclizations of 3 , 14 , 18 and 21 with Mn(OAc) 3 ·2H 2 O give the tricyclic products 6 , 15 , 19 and 23 , respectively, in good yield. These reactions proceed through a monocyclic secondary radical which adds to the benzene ring prior to the second oxidation.