Dialkyl carbonates, protonation

Carbonic acid and dialkyl carbonates are also carbonyl-protonated in HSO3 F—SbFj —SO2 low temperature (Olah and White, 1968). 

Carbonic acid and dialkyl carbonates are also carbonyl-protonated in HS03 F—SbFs —S02 at low temperature (Olah and White, 1968). The trihydroxycarbonium ion [207] is stable up to 0°C in the absence of S02. This and analogous ions formed by the protonation... 

Dialkyl carbonates have been studied in FSO3H—SbFs solution and have been shown to be protonated on the carbonyl group giving the dialkoxyhydroxy methyl cation168. ... 

The ratio ARH/ARj (monoalkylation/dialkylation) should depend principally on the electrophilic capability of RX. Thus it has been shown that in the case of t-butyl halides (due to the chemical and electrochemical stability of t-butyl free radical) the yield of mono alkylation is often good. Naturally, aryl sulphones may also be employed in the role of RX-type compounds. Indeed, the t-butylation of pyrene can be performed when reduced cathodically in the presence of CgHjSOjBu-t. Other alkylation reactions are also possible with sulphones possessing an ArS02 moiety bound to a tertiary carbon. In contrast, coupling reactions via redox catalysis do not occur in a good yield with primary and secondary sulphones. This is probably due to the disappearance of the mediator anion radical due to proton transfer from the acidic sulphone. 

Michael addition in the absence of any catalytic agent has been reported for dialkyl and diaryl phosphites and thiophosphites with a-cyanoacrylate esters and a-cyanoacrylic acid.444 Yields of the conjugate addition products were moderate to good. The regiochemistry of this process is the opposite of that previously reported for similar additions to ketene acetals, the latter presumably proceeding by initial protonation of the distal olefinic carbon site.445... 

Overall, the process requires the consumption of two electrons and two protons. The structure and acidity of effective proton donors vary from mineral to carbon acids often, a simple dialkyl malonate is effective. It is easy to monitor current consumption using a simple, commercially available coulometer [3,4]. 

The voltammetric reduction of a series of dialkyl and arylalkyl disulfides has recently been studied in detail, in DMF/0.1 M TBAP at the glassy carbon electrode The ET kinetics was analyzed after addition of 1 equivalent of acetic acid to avoid father-son reactions, such as self-protonation or nucleophilic attack on the starting disulfide by the most reactive RS anion. Father-son reactions have the consequence of lowering the electron consumption from the expected two-electron stoichiometry. Addition of a suitable acid results in the protonation of active nucleophiles or bases. The peak potentials for the irreversible voltammetric reduction of disulfides are strongly dependent on the nature of the groups bonded to the sulfur atoms. Table 11 summarizes some relevant electrochemical data. These results indicate that the initial ET controls the electrode kinetics. In addition, the decrease of the normalized peak current and the corresponding increase of the peak width when v increases, point to a potential dependence of a, as discussed thoroughly in Section 2. 

O-protected cyclic or acyclic carbon frameworks. The choice of acetals or ethers as derivatives allows a systematic manipulation of diols and polyols. Kinetic control and a lesser affinity for protonation on sulfur compared with oxygen allows the transformation of cyclic hemiacetals into acyclic dialkyl dithioacetals. Acetal, ether, and dithioacetal derivatives are some of the pivotal intermediates needed to explore various applications of carbohydrates in synthesis. 

Alcohols will add to allenes in the presence of trace amounts of acids to give vinyl ethers (or acetals) or allylic ethers.401 Analogous to the hydration of allenes, protonation occurs on the terminal carbon of the allenic functionality in 1,2-propadiene, 3-alky 1-1,2-propadienes and 1,3-dialkyl- 1,2-propadienes (equation 248).402 Addition of an alcohol to the resulting vinylic cation produces a vinylic ether, which may on further reaction form an acetal of the corresponding ketone. 

A study of the mono- vs di-alkylation reactions of dibromide (9) with carbanions (lOc-g), covering a range of >15 pK units in DMSO, has revealed that the carbanions (lOd-g) derived from the less acidic carbon acids give exclusively the bis(monoalkylated) product (ii) however, carbanions (lOa-c) give the cyclic product (12) of dialkylation.21 This dichotomy is apparently a consequence of the relative rates of formation (by proton transfer, /id) and cyclization (kc) of die conjugate base of the monoalkylated intermediate. 

The sodium salts of dialkyl l-(alkoxycarbonyl)methylphosphonates. in the presence of a further equivalent of NaH, undergo addition of carbon disulfide in EtjO at room temperature to give alkenedithiolates, which are characterized by protonation, alkylation (Mel, EtI, BnCl), oxidation, and phosgenation. For example, reaction with metliyl iodide provides the dialkyl 1-alkoxycarbonyl-2,2-/7i.v(mcthylthio)vinylphosphonates in good yields (68-75%), whereas room-temperature treatment with acetyl or benzoyl clilonde produces l,3-dithietane-2,4-diylidene-foZ5 [(alkoxycarbo-nyl)methylphosphonates] in moderate yields (18-39%, Scheme 8.23). The same oxidation product is obtained by reaction with iodine. 

Reactions of Phosphines. - 1.2.1 Nucleophilic Attack at Carbon. Interest has continued in developing the synthetic applications of the 1 1 adducts of tertiary phosphines with dialkyl acetylenedicarboxylate esters. Protonation of the initial adduct from triphenylphosphine by phthalimide, followed by nucleophilic addition of the nitrogen of the resulting imido anion to the intermediate vinylphosphonium salt, has given the stabilised ylide system (189). ° Similar reactions with isatin and 3-chlorotetrahydrofuran-2,4-dione have given the yl-... 

The addition of HX reagents to dialkyl(methylthioethynyl)phosphine oxide (32) under acidic or basic conditions results in protonation of the triple bond on the carbon adjacent to phosphorus. It would appear that the phosphoryl... 

---