Donor substituted sulfonyl carbenes, 2: Organothio sulfonyl carbenes

Abstract

Organothio sulfonyl carbenes 3 have been generated via ylid thermolysis or via α-elimination starting from α-chloro α-organothio sulfones and their derivatives. They have been captured by suitable nucleophilic trapping reagents (diazomethane, enol ethers, and others). Their nucleophilic carbenoid precursors could be trapped by an electrophilic olefin (ketene dithioacetal S,S-dioxides as Michael acceptors). Stable carbene Z-dimers could be obtained under various conditions. Bromine catalyzed isomerization to E-isomers proved to be reversible.

Synthesis and Biological Evaluation of Novel Epothilone B Side Chain Analogues

“…Scheme 1s ummarizes the synthesis of Teoc-and Boc-protected aminoethyl pyrazole epothilone analogues 5-7 from the readily availableb uildingb locks 3-(methylthio)-1H-pyrazole (16 a) [7] and commercially available 3-(trifluoromethyl)-1H-pyrazole (16 b). Thus, alkylation of 16 a with N-Boc bromide 17 a (prepared from the corresponding commerciallya vailable bromoamine by the standard method) [8] under basic conditions (NaH) led to pyrazole derivative 18 a (74 %y ield), whichwas regioselectively stannylated through lithiation( nBuLi)f ollowed by addition of nBuSnCl (38 %y ield).…”

Photochemical Alkylation of Ketene Dithioacetal S,S-Dioxides. An Example of Captodative Olefin Functionalization

“…These, in turn, are convenient synthetic intermediates in view of several possible elaborations, e.g., C -alkylation and -arylation, substitution of an allyl for a sulfone group, desulfurization, , pyrolysis to yield a carbonyl derivative, Pummerer rearrangement . Ketene dithioacetal S , S -dioxides have been shown to act as efficient acceptors of carbenes as well as of 1-hydroxy- (or alkoxy-)alkyl radicals. , Furthermore, intramolecular radical addition of β-(ω-iodoalkyl) derivatives has been shown to occur under classic radical chain conditions yielding five-, six-, and also four-membered cyclic derivatives, a result rationalized on the basis of the peculiar stability of the adduct radical due to the captodative effect . Somewhat surprisingly, no corresponding intermolecular radical alkylation has been reported except for the above-mentioned case of hydroxyalkyl radicals.…”