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An alkene bearing two thioalkoxy groups on one carbon, ${\mathrm{R}}_2\mathrm{C}=\mathrm{C}(SR\prime {)}_2$. pi conjugation to a carbonyl can allow addition–elimination at that beta carbon with thiolate departure.

A nitroalkane carbon can join the two ends of a five-carbon conjugated ketone framework. carbon–carbon bond formation, thiolate displacement and nitrite elimination can build a substituted phenol. The nitro-bearing carbon, rather than the nitro nitrogen, enters the aromatic ring.

A is a fused five-/six-membered bicyclic diketone containing sulfur. To specify its structure unambiguously, retain the cyclohexanone numbering C1=O, C2 and C3 for the original alkene. Add the five-membered ringThe original C1 ketone remains, and the former methyl-ester carbonyl becomes the second ketone. The product is drawn in the first panel below.

methoxide first deprotonates the thiol. The soft thiolate attacks the beta carbon C3 in a Michael addition, shifting the enone electrons onto oxygen. The resulting enolate is nucleophilic at C2. It then attacks its tethered ester carbonyl intramolecularly, forming a five-membered ring through a tetrahedral intermediate. Collapse expels methoxide. proton transfers and work-up give the neutral bicyclic beta-diketone.

The initial 1,4 addition followed by intramolecular Claisen acylation explains the regiochemistry: it connects C3 to sulfur and C2 to the ester carbonyl, giving a favorable five-membered closure. Addition to the original ketone would not give this same enolate-and-ester arrangement. The net loss of methanol from the combined starting materials gives the observed ${\mathrm{C}}_8{\mathrm{H}}_{10}{\mathrm{O}}_2\mathrm{S}$ formula.

sulfide first opens one epoxide by backside attack, giving a carbon-bound thiolate and an alkoxide. Using the same numbering, take this first attack at C2: the C2–S bond is down and C3–O remains up.

The attached sulfur still bears a nucleophilic lone pair and negative charge. It attacks C5 of the second epoxide intramolecularly, breaking C5–O and closing a bridge between C2 and C5. Work-up protonates the oxygen anions at C3 and C6. Thus B is 7-thiabicyclo$[\mathrm{2.2.1}]$heptane-2,5-diol, with both OH groups on the face opposite the sulfur bridge.

Both C–S bonds are formed by inversion at their attacked epoxide carbons. Because the original epoxides are cis, both new C–S bonds point to the same opposite face and one sulfur chemical atom can connect them. The 1,4 bridge gives two five-membered sulfur-containing circuits, unlike the more strained closure between nearby 1,3 positions.

The sulfur therefore replaces two separate external nucleophiles: two epoxides are opened but only one sulfur chemical atom is incorporated. Adding that sulfur and two work-up protons gives ${\mathrm{C}}_6{\mathrm{H}}_{10}{\mathrm{O}}_2\mathrm{S}$, consistent with B.

Cleavage of the disulfide supplies one methylthiolate per cobalt. A monomer $\mathrm{CpCo}(\mathrm{SMe})$ would have only $7+6+2=15$ electrons by ionic counting. Dimerization with two bridging thiolates supplies a second sulfur interaction at each cobalt, and a direct Co–Co bond completes each count. Thus a suitable structure is $[\mathrm{CpCo}(\mu \text{-}\mathrm{SMe}){]}_2$ with a Co–Co single bond, containing an $\mathrm{C}{\mathrm{o}}_2{\mathrm{S}}_2$ diamond:Each cobalt is formally $+2$: Cp and methylthiolate each carry one negative charge. The stoichiometry isThe molecular formula ${\mathrm{C}}_{12}{\mathrm{H}}_{16}\mathrm{C}{\mathrm{o}}_2{\mathrm{S}}_2$ reduces to the required empirical formula. The sulfur–sulfur bond has been cleaved, both sulfur atoms now bridge the metals, and the loss of two CO molecules per cobalt is balanced. Formally cobalt(I) is oxidized to cobalt(II), while the disulfide is reduced to thiolate.

Distinguish the original thiirane sulfur $S_o$ from the sulfur $S_n$ supplied by thiocyanate. sulfur attack by ${}^{-}{\mathrm{S}}_{\mathrm{n}}-\mathrm{C}\equiv \mathrm{N}$ at one thiirane carbon opens its C–$S_o$ bond with inversion. This produces a thiolate at the neighbouring carbon and a C–$S_n$–CN group at the attacked carbon. The OH-bearing remote carbon is unaffected.

The original thiolate $S_o^{-}$ now attacks the nitrile carbon intramolecularly. Shift one C≡N pi pair onto nitrogen. The resulting cyclic imidodithiocarbonate has the five-membered sequence ring carbon–$S_o$–C(=N${}^{-}$)–$S_n$–adjacent ring carbon; its two carbon atoms are also part of the original six-membered carbocycle, exactly giving the hinted bicyclic intermediate.

Collapse can reform C≡N while breaking the nitrile-carbon–$S_n$ bond. This transfers the CN group to $S_o$ and generates $S_n^{-}$ as the thiolate on the other ring carbon. That thiolate attacks the remaining C–$S_o$ bond from the back, expelling ${}^{-}{\mathrm{S}}_{\mathrm{o}}-\mathrm{C}\equiv \mathrm{N}$ and reclosing the thiirane. Each thiirane carbon has undergone one inversion, so the new sulfur bridge lies on the opposite face; the OH configuration is retained. The thiocyanate sulfur has entered the ring and the original ring sulfur has left as thiocyanate. This atom-labelled exchange mechanism explains how the same elemental formula can conceal sulfur replacement; isotope labelling would be needed to test that exchange experimentally. A single epimerization at the OH carbon would give the wrong stereochemical outcome.

With triethylamine present, proton transfer from thiophenol produces a more nucleophilic thiolate population. sulfur attacks the anomeric epoxide carbon C1 from the face opposite its epoxide C–O bond. Displacement by backside attack opens the epoxide, breaks C1–O, and leaves the former epoxide oxygen attached to C2. protonation of that alkoxide by thiophenol or triethylammonium gives G: SPh at C1 on the front face and OH at C2 on the back face, a trans relationship. This is inversion at C1 with retention of the C2 C–O bond; there is no need to invert every stereocentre. Rapid protonation also suppresses competing silyl transfer by the alkoxide.

Without added base, neutral thiophenol is less nucleophilic. acid-assisted cleavage at the anomeric epoxide bond can instead be accompanied by donation from the ring oxygen, giving an oxocarbenium ion with charge shared with the ring oxygen. thiophenol capture from the face that puts SPh back on the original epoxide face, followed by deprotonation, gives H with SPh and C2–OH both on the back face, the net-retention pathway. An ion-pair or highly asynchronous opening can provide this outcome; the drawing does not establish a long-lived free carbocation.

The distinction is configuration, not a mandatory fixed chair. For the closely matching trisilylated substrate, the primary study obtained both anomers with thiophenol alone, and established an unusual inverted chair for the alpha thioglycoside by NMR and crystallography. Thus H should be explained as an accessible product, not asserted to be the sole product or necessarily to have axial SPh in its preferred conformation.^[ref]

Base again generates $\mathrm{Ph}{\mathrm{S}}^{-}$ catalytically. In $\mathrm{P}{\mathrm{h}}_2\mathrm{P}(\mathrm{O})-\mathrm{CH}=\mathrm{C}=\mathrm{C}{\mathrm{H}}_2$, attack at the central allene carbon moves the adjacent C=C pi electrons onto the phosphorus-bearing carbon. This makes the stabilized alpha-phosphoryl carbanionprotonation at that carbon gives $\mathrm{P}{\mathrm{h}}_2\mathrm{P}(\mathrm{O})-\mathrm{C}{\mathrm{H}}_2-\mathrm{C}(\mathrm{SPh})=\mathrm{C}{\mathrm{H}}_2$, the second product drawn above. The remaining double bond is terminal, so no E/Z pair is possible. The new sulfur bond is at the central carbon of the original allene, not at the terminal methylene.

This regiochemistry places the developing negative charge beside the electron-withdrawing phosphine-oxide group, instead of at a less stabilized vinylic position. It is an ionic addition/proton-transfer cycle, rather than radical thiol–ene chemistry. proton donation by another thiophenol molecule regenerates thiolate. One thiophenol is incorporated without loss of atoms, giving ${\mathrm{C}}_{21}{\mathrm{H}}_{19}\mathrm{OPS}$.

Hydroxide initially deprotonates a little thiophenol, generating the reactive thiolate $\mathrm{Ph}{\mathrm{S}}^{-}$. Number the extended conjugated system $\mathrm{O}=C1-C2=C3-C4=C5$, where C1–C2–C3 is the ring enone and C4=C5 is the attached vinyl group. sulfur attacks the terminal delta carbon C5. The pi bonds relay toward oxygen, generating an extended enolate.

proton transfer at C4, either directly from thiophenol or through solvent-mediated enolization, gives the product retaining the conjugated ring enone. The product is 3-[2-(phenylsulfanyl)ethyl]cyclohex-2-en-1-one, drawn below. Its side chain is $-\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{SPh}$; the ring C2=C3 double bond remains. This is net sulfur/hydrogen addition to the terminal part of the extended system, proceeding through 1,6-Conjugate addition and protonation of the extended enolate.

The terminal site is less crowded than the ring beta carbon, and the isolated product retains favorable carbonyl–alkene conjugation. Reversible proton transfers and conjugate addition under thiolate catalysis can favor that product over an unconjugated enone-derived alternative. Transfer of a proton from another PhSH molecule regenerates PhS${}^{-}$, explaining why a catalytic quantity of hydroxide suffices. The net balance is one thiophenol added, ${\mathrm{C}}_8{\mathrm{H}}_{10}\mathrm{O}+{\mathrm{C}}_6{\mathrm{H}}_6\mathrm{S}={\mathrm{C}}_{14}{\mathrm{H}}_{16}\mathrm{OS}$; carbonyl 1,2 addition would instead produce a different functional group and is not favored for this soft sulfur nucleophile.

A thiolate is $\mathrm{R}{\mathrm{S}}^{-}$, the conjugate base of a thiol. Its polarizable sulfur is often effective in conjugate addition. protonation of the resulting carbon anion can regenerate thiolate from another thiol molecule.

A pair of metal centres connected through one or more thiolate sulfur donors. A ${\mathrm{M}}_2(\mu -\mathrm{SR}{)}_2$ diamond can coexist with a direct metal–metal bond; each bridging thiolate supplies a donor interaction at both metals.