2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) has long been recognized as a versatile organic oxidant that mediates diverse transformations through single-electron transfer, hydride abstraction, and redox cycling. Beyond its classical stoichiometric role in oxidation and dehydrogenation, DDQ now serves as an efficient catalyst for carbon-carbon bond formation across thermal, photochemical, and electrochemical domains. In stoichiometric reactions, DDQ enables benzylic and allylic CH activation to generate oxocarbenium or iminium intermediates that couple with a broad range of nucleophiles, facilitating alkylation, arylation, cyanation, and annulation processes. In catalytic systems, DDQ participates in redox cycles where the DDQ/DDQH₂ couple is regenerated by oxidants such as O₂, nitrites, or MnO₂, offering mild and simple access to complex carbon frameworks. The scope further extends to asymmetric catalysis and radical-mediated cross-dehydrogenative coupling, providing sustainable routes to natural product-like scaffolds and biologically active molecules. This review highlights the progression of DDQ from a stoichiometric oxidant to a redox-active catalyst, emphasizing its growing utility in controlled, metal-free oxidative CC bond formation and its promise for next-generation sustainable synthesis.

These values are given in the following table. | R (in R–H) | methyl | ethyl | i-propyl | t-butyl | phenyl | benzyl | allyl | vinyl | |---|---|---|---|---|---|---|---|---| | Bond Dissociation Energy (kcal/mole) | 103 | 98 | 95 | 93 | 110 | 85 | 88 | 112 | The difference in C-H bond dissociation energy reported for primary (1º), secondary (2º) and tertiary (3º) sites agrees with the halogenation observations reported above, in that we would expect weaker bonds to be broken more easily than are strong bonds. By this reasoning we would expect benzylic and allylic sites to be exceptionally reactive in free radical halogenation, as experiments have shown. The methyl group of toluene, C6H5CH3, is readily chlorinated or brominated in the presence of free radical initiators (usually peroxides), and ethylbenzene is similarly chlorinated at the benzylic location exclusively. The hydrogens bonded to the aromatic ring (referred to as phenyl hydrogens above) have relatively high bond dissociation energies and are not substituted.

Since carbon-carbon double bonds add chlorine and bromine in liquid phase solutions, radical substitution reactions by these halogens are often carried out at elevated temperature in the gas phase (first equation below). Formation of the ionic π-complexes that are intermediates in halogen addition is unfavorable in the absence of polar solvents, and entropy generally favors substitution over addition. The brominating reagent, N-bromosuccinimide (NBS), has proven useful for achieving allylic or benzylic substitution in CCl4 solution at temperatures below its boiling point (77 ºC). One such application is shown in the second equation. The predominance of allylic substitution over addition in the NBS reaction is interesting. The N–Br bond is undoubtedly weak (probably less than 50 kcal/mol) so bromine atom abstraction by radicals should be very favorable. The resulting succinimyl radical might then establish a chain reaction by removing an allylic hydrogen from the alkene. One problem with this mechanism is that NBS is very insoluble in CCl4, about 0.006 mole / liter at reflux.

particularly suitable for primary, allylic, and benzylic halides. Secondary alkyl halides provide lower yields, whereas tertiary halides undergo exclusively In organic chemistry, a nitrile is any organic compound that has a −C≡N functional group. The name of the compound is composed of a base, which includes the carbon of the −C≡N, suffixed with "nitrile", so for example CH3CH2C≡N is called "propionitrile" (or propanenitrile). The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful co Similarly, 1,3-dibromopropane reacts with sodium cyanide to form glutaronitrile, and 1-iodooctane reacts with potassium cyanide to give nonannitrile. Cyanations can also be carried out using hydrogen cyanide in combination with triethylaluminum or with diethylaluminum cyanide; for example, in the ring opening of an epoxide to a β-cyanohydrin or in the 1,4-addition of cyanide to an enone. Trimethylsilylcyanide is another cyanating reagent capable of opening epoxides to β-cyanohydrins, with concomitant silylation of the oxygen atom. Trimethylsilyl cyanide also enables substitution of tertiary alkyl halides, which is not feasible under Kolbe nitrile synthesis conditions. In the presence of suitable transition metal catalysts, hydrocyanation allows addition of hydrogen cyanide to the multiple bonds of alkenes and alkynes to afford nitriles. Nickel catalysts are typically employed. Direct handling of hydrogen cyanide is often unnecessary, as synthetic equivalents such as acetone cyanohydrin or… Numerous traditional methods exist for nitrile preparation by amine oxidation. Common methods include the use of potassium persulfate, Trichloroisocyanuric acid, or anodic electrosynthesis. In addition, several selective methods have been developed in the last decades for electrochemical processes. Several procedures employ nitroxyl radicals such as TEMPO or 4-acetamido-TEMPO as catalytic oxidants. These catalysts can be regenerated either by potassium peroxymonosulfate as the stoichiometric oxidant or electrochemically under applied potential. Another approach utilizes copper(I) chloride or copper(II) chloride as catalyst, molecular oxygen as the stoichiometric oxidant, and a molecular sieve to remove the water formed. Nitriles are susceptible to hydrogenation over diverse metal catalysts. The reaction can afford either the primary amine (RCH2NH2) or the tertiary amine ((RCH2)3N), depending on conditions. In conventional organic reductions, nitrile is reduced by treatment with lithium aluminium hydride to the amine. Reduction to the imine followed by hydrolysis to the aldehyde takes place in the Stephen aldehyde synthesis, which uses stannous chloride in acid. A few dozen…

Alkyl organoboron compounds are versatile synthons in organic synthesis, enabling rapid access to a variety of carbon─carbon and carbon-heteroatom bonds. As such, strategies to efficiently access carbon-boron bonds from simple chemical feedstocks are highly desirable. The radical borylation of alkyl bromides presents an attractive approach. However, the activation of alkyl bromides typically requires strong reductants or transition-metal catalysts. Herein, we report a metal-free radical borylation strategy of various alkyl bromides utilizing a photoinduced silyl radical to mediate a halogen-atom transfer process. This method demonstrates broad utility and functional group tolerance among various primary, secondary, and tertiary unactivated alkyl bromides and can facilitate the functionalization of pharmaceutically relevant motifs. Mechanistic and computational studies support a radical-chain pathway involving a silyl radical-mediated halogen-atom transfer.