B. S. Thyagarajan

Control of Regiochemistry, Stereochemistry and Stoichiometry in Additions to Alkadiynes. Synthetic Value of a Sulfone Function

Abstract The strategic placement of a sulfone function alpha to a conjugated alkadiyne is shown to enforce total control of regiochemistry, stereochemistry and stoichiometry in additions of nucleophiles across the triple bonds.

Thiol additions to 1,4-diarylsulfonyl-2 butynes. Stereochemistry of addition and regiospecific eliminations from the adducts

Abstract Thiol additions to 1,4-diarylsulfonyl-2-butynes result in stereoselective formation of 1,4-diarylsulfonyl-2-arylthio-2-butenes with a preponderance of the E isomer over the Z. Contrary to the behaviour of similar adducts from 1-arylsulfonyl-4-(N′-anilino)-2-butynes and 1-arylsulfonyl-4-arylthio-2-butynes, the vinyl sulfides obtained from the diarylsulfonylbutynes undergo facile isomerization under mild base catalysis. A regiospecific elimination followed by readdition is shown to be the mechanism for such isomerizations.

STEREOSELECTIVE ADDITION OF ARENE THIOLS TO 1,4-DISUBSTITUTED-2-BUTYNES

Abstract Base-catalyzed addition of arene thiols to 1,4-disubstituted-2-butynes (1 and 2) afford the β,γ-unsaturated sulfones (8E and 8Z). In addition to the regiospecificity observed, the vinyl sulfides are formed with a high degree of stereoselectivity. Product formation through a less-hindered approach by the nucleophile appears to favor the E over the Z isomer, consistently in all the 11 cases investigated.

NOVEL SYNTHESIS OF THIAZOLIDINES

Abstract A novel synthesis of thiazolidine derivatives is described, based on nucleophilic additions across the triple bond of 1,4-diarylsulfonyl-2-butynes. The use of bidentate nucleophiles like N,N′-dialkylthioureas, under mild base catalysis, at ambient conditions affords good yields of the title compounds. A mechanism for the formation of the compounds is offered and supported by appropriate experiments.

Thiol Additions To Dissymmetrical 1,4-Diary Sulfonyl-2-Butynes Regioselectivity And Stereoselectivity

Abstract Regioselectivity is restored in the addition of thiols to 1,4-diarylsulfonyl-2-butynes based on differing electron-demands of the substituents on the aromatic rings attached to the butynyl sulfones. Kinetic control of addition leading to preponderant formation of the less stable vinyl sulfide with an E geometry is observed. Thermodynamic stability favors the Z isomer of the vinyl sulfide. The results are consistent with and confirm the rationale proposed earlier, implicating the intermediacy of an allene.

1,4-DIARYLSULFONYL-1,3-BUTADIENES FROM 1,4-DIARYLSULFONYL-2-BUTYNES

Abstract Isomerization of 1,4-diarylsulfonyl-2-butynes under aprotic conditions and ambient temperatures with mild base catalysis leads to the title compounds.

DICHOTOMY IN THE ISOMERIZATIONS OF 1-ARYLSULFONYL-3-ARYLTHIO-2-BUTENES AND DERIVATIVES THEREOF

Abstract A dichotomy in the mechanism for the isomerizations of the title compounds is describedy An elimination-readdition pathway promotes isomerization of 1,4-diarylsulfonyl-2-arylthio-2-butenes and 1,2,4-triarylthio-2-butenes. However, 1-arylsulfonyl-3-arylthio-2-butenes and 1,3-diarylsulfonyl-2-butenes require stronger bases and more polar solvents for isomerization and occur without any eliminations.

A Novel Application of Sodium Borohydride for the Regiospecific and Stereoselective Reduction of Conjugated Alkadiynes

Abstract Alkynes, when carrying an α-sulfonyl group, are shown to be stereoselectively reduced to z-alkenes using sodium borohydride under mildly basic conditions.

ANIONIC ADDITIONS TO CONJUGATED ENYNES—UNUSUAL DISPLACEMENTS OF VINYLIC SULFONES

Abstract Reaction of sodium benzenesulfinate with 1,2-di(4-chloro-benzenesulfonyl)-2-hexen-4-yne affords not only the regiospecific addition of the nucleophile at Carbon-5 but also effects concomitant vinylic and allylic displacements at Carbons-1 and 2

Concurrent configurational modification in conjugated dienes; a new pathway in the isomerization of alkadienes

The hexa-2,4-diene derivative (2), obtained from 1,6-di(phenylsulphonyl)hexa-2,4-diyne (1), is shown to undergo simultaneous Isomerization at both double bonds, through an elimination-addition pathway.