BCl₃‐Mediated Ene Reaction of Sulfur Dioxide and Unfunctionalized Alkenes

Abstract

The first ene reactions of SO(2) and unfunctionalized alkenes are reported. Calculations suggest that the endergonic ene reactions of SO(2) with alkenes can be used to generate beta,gamma-unsaturated sulfinyl and sulfonyl compounds. Indeed, in the presence of one equivalent of BCl(3), the unstable sulfinic acid form stable sulfinic acid.BCl(3) complexes that can be reacted in situ with NCS to generate corresponding sulfonyl chlorides, or with a base to generate corresponding sulfinates. The latter can be reacted with electrophiles to generate sulfones, or with silyl chloride to form beta,gamma-unsaturated silyl sulfinates. The sulfinic acid.BCl(3) complexes can be reacted with ethers that act as oxygen nucleophiles to produce corresponding sulfinic esters. Thus one-pot, three-component synthesis of beta,gamma-unsaturated sulfonamides, sulfinyl esters and sulfones have been developed starting from alkenes and sulfur dioxide (reagent and solvent).

Rediscovering the Chemistry of Sulfur Dioxide: New Developments in Synthesis and Catalysis

“…Vogel has developed this chemistry further with the advent of a bora-ene reaction of unfunctionalised alkenes employing boron trichloride and an excess of sulfur diox-ide (Scheme 12). 69 The BCl 3 -sulfinic acid generated in situ was applied in the synthesis of a range of allyl sulfonyl and sulfinyl compounds. This chemistry has also been explored with prop-2-ene boronic esters with the corresponding mixed sulfinic-boric anhydride trapped in situ with Grignard reagents, delivering sulfoxide products.…”

The Catalyzed Desulfinylative Allylation of Carbonyl Compounds with Alk‐2‐enesulfonyl Chlorides and Silyl Alk‐2‐enesulfinates

“…[29,30] As these compounds can also be obtained by the H-ene reaction of alkenes with SO 2 /BCl 3 , followed by neutralization with NH 3 and reaction with silyl chlorides [10] (Scheme 5), we wondered whether these systems could be employed as nucleophilic allylating agents.…”

“…[8] We have also shown that 2-methylprop-2-ene-(1), prop-2-ene-(3), and (E)-but-2-enesulfonyl chlorides (4) are useful electrophilic partners in desulfinylative palladium-catalyzed C À C coupling reactions with inexpensive Grignard reagents and sodium salts of malonic esters and methyl acetoacetate. [9] As these sulfonyl chlorides can be prepared in one-pot operations (Scheme 1) through a BCl 3 -promoted ene reaction of the corresponding monoalkenes with sulfur dioxide, [10] substrates 1-4 have become powerful electrophilic allylating agents (without BCl 3 , the ene reaction of simple monoalkenes with SO 2 is endergonic above À100 8C). [11] We have recently reported that iron catalysts can be used in the desulfinylative CÀC cross-coupling reaction of Grignard reagents with alkane-, alkene-, and arenesulfonyl chlorides [12] and with alk-3-enesulfonyl chlorides.…”

Visible-light-induced one-pot synthesis of sulfonic esters via multicomponent reaction of arylazo sulfones and alcohols

“…Besides, in the synthesis of compounds containing sulfonic esters, several preparation procedures utilize sulfur dioxide (SO 2 ). 12 SO 2 is a crucial intermediate in organic synthesis with advantages including its prevalence in nature, affordable cost, and ease of transformation to the sulfonyl structural moiety. 13 Therefore, SO 2 has been extensively used as a sulfonyl precursor in organic chemistry for several decades.…”