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The preparation of 27 isomers of chiral hexahalogeno-4,4′-bipyridines by means of two complementary methods is described. The first one is convergent and based on the LDA-induced 4,4′-dimerization of trihalopyridines, whereas the second method is divergent and achieved through regioselective halogenation reactions of 4,4′-bipyridine-2,2′-diones. Iodine in 2,2′-positions of the 4,4′-bipyridines was introduced by a copper-catalyzed Finkelstein reaction (Buchwald procedure) performed on 2,2′-dibromo derivatives. Selected compounds of this new family of atropisomeric 4,4′-bipyridines were enantioseparated by high performance liquid chromatography on chiral stationary phases, and the absolute configurations of the separated enantiomers were assigned by using X-ray diffraction analysis. The latter revealed that various halogen bond types are responsible for crystal cohesion.

Lithiation of the achiral tetrahalogenated 4,4′-bipyridine 1 with alkyllithiums was investigated. n-BuLi was found to induce either the chlorine-directed deprotolithiation reaction alone or with a concomitant halogen–lithium exchange furnishing after iodine trapping chiral 4,4′-bipyridines 2 and 6, respectively. The role of n-BuLi in the deprotolithiation process of 1 was elucidated on the basis of isolated secondary derivatives. After deprotolithiation, the lithiated species could be trapped by different electrophiles such as MeI, TMSCl, MeSSMe, R3SnCl (R = Me or n-Bu), and PPh2Cl. Moreover, 4,4′-bipyridine 2 was submitted to cross-coupling reactions (Suzuki and Sonogashira) which occurred selectively at the carbon–iodine bond. All compounds of this new family of atropisomeric 4,4′-bipyridines were separated by chiral HPLC (high-performance liquid chromatography), and the absolute configurations of obtained enantiomers were mainly assigned by XRD (X-ray diffraction) using anomalous dispersion.

Five synthetic routes have been evaluated for the regioselective preparation of (R)-5-methyl- and (R)-7-methyl-5,6,7,8-tetrahydroquinolines from (+)-(R)-3-methylcyclohexanone

(1991). A RAPID PREPARATION OF 2,2′-DIMERCAPTOBIPHENYL. Organic Preparations and Procedures International: Vol. 23, No. 4, pp. 455-457.

General and convenient syntheses of optically active 5-alkylpiperazine- 2-carboxylic acids are described. The methods are based on cyclization of L- or D-serine with α-amino acids and occur without loss of optical purity. The presented procedures are based on readily available starting materials and can be arranged for multigram quantities

2-Chloro-1,4-benzodithiin 1,1,4,4-tetraoxide 11 is a reactive dienophile that forms Diels-Alder adducts with a number of dienes. Adducts 17a–j undergo facile dehydrochlorination to give 2,3-substituted 1,4-benzodithiin tetraoxides 18a–j, which react further with another molecule of diene (the same or a different one) affording the “double” adducts 19-23. Upon reductive desulfonylation with sodium amalgam, the latter are transformed to tetrasubstituted polycyclic olefins 24-27. These olefins correspond to the cycloadducts that would theoretically have been formed by the cycloaddition of diatomic carbon with two molecules of diene, reacting in a Diels-Alder fashion.

We introduce a new class of arylsulfonylated cyclic acetals derived from carbohydrate structures which are synthesized with high yields under basic conditions. Deprotection methods for such acetals are also investigated. © 2000 Elsevier Science Ltd. All rights reserved.

A range of sugar-derived phenylsulfonylethylidene acetals were easily obtained from the corresponding diols and 1,2-bis(phenylsulfonyl)ethylene under basic conditions. Deprotection methods for such acetals have also been investigated.

The preparation of the title compounds (Z)- and (E)-1, which are synthetic substitutes for the unstable bis(phenylsulfonyl) acetylene and key reagents for the asymmetric preparation of polycyclic ketones, has been revisited and improved. Starting from inexpensive materials such as trichloroethylene, thiophenol, and hydrogen peroxide, (Z)- and (E)-1 are selectively obtained in multigram quantity in 52% overall yields.

Addition-elimination of an alcohol to 1,2-bis(phenylsulfonyl)ethylene afforded β-alkoxyvinyl sulfones which were submitted to reductive elimination with 6% sodium amalgam to produce the corresponding ethenyl ethers in high yields and purity.

A stereoselective desymmetrization is a symmetry breaking synthetic operation and represents a powerful synthetic tool not only for the preparation of new chiral synthons or building blocks, but also for the applications in the target oriented synthesis, yielding enantiomerically enriched products. In this microreview, after a brief historical overview of the origin of the method, through representative examples that go back to the last six years, we describe the role of molecular symmetry and steric effects on the stereotopic and stereofacial discrimination mechanisms. The most effective procedures to perform a stereoselective desymmetrization of a non chiral symmetric compound by nonenzymatic or enzymatic methods are here presented.

The synthetic potential of bis(phenylsulfonyl)alkenes, especially in view of their ability to function as equivalents of acetylene in cycloaddition reactions for the preparation of polycyclic molecules, is discussed. Differently from the bis(phenylsulfonyl)alkenes, bis(phenylsulfonyl)-acetylene has to be prepared and reacted in situ and affords polycyclic bis(phenylsulfonyl)alkenes upon Diels-Alder reaction. The same products arising from bis(phenylsulfonyl)acetylene can be more products arising from bis(phenylsulfonyl)acetylene can be more conveniently prepared by cycloaddition of (E)-1-chloro-1,2-bis(phenylsulfonyl)ethylene and dehydrochlorination with triethylamine. They react with enantiopure C2-symmetric diols with complete enantiotopic discrimination, eventually leading to polycyclic enantiopure ketones of known configuration. The enantiopure ketones, transformed into bromoalkenes, are further transformed into bromotrimethylstannyl alkenes. Upon treatment with copper nitrate trihydrated, the latter ...