Notes: Reactions of Alkyl Phosphites with Diethyl Azodicarboxylate

Electrochemical Azo-free Mitsunobu-type Reaction

The classic chemical Mitsunobu reaction suffers from the need of excess alcohol activation reagents and the generation of significant by-products. Efforts to overcome these limitations have resulted in numerous creative solutions, but the substrate scope of these catalytic processes remains limited. Here we report an electrochemical Mitsunobu-type reaction, which features azo-free alcohol activation and broad substrate scope. This user-friendly technology allows a vast collection of heterocycles as the nucleophile, which can couple with a series of chiral cyclic and acyclic alcohols in moderate to high yields and excellent ee's. This practical reaction is scalable, chemoselective, uses simple Electrasyn setup with inexpensive electrodes and requires no precaution to exclude air and moisture. The synthetic utility is further demonstrated on the structural modification of diverse bioactive natural products and pharmaceutical derivatives and its straightforward application in a multiple-step synthesis of a drug candidate.

Alkylphosphinites as Synthons for Stabilized Carbocations

We present a new acid-free method for the generation of carbocations based on a redox condensation reaction that enables S_N1 reactions with a variety of nucleophiles. We utilize readily synthesized phosphinites that are activated by diisopropyl azodicarboxylate to form betaine structures that collapse upon adding a pronucleophile, thereby yielding reactive carbocation intermediates. We also employ this approach for the alkylation of some bioactive molecules.

Radical reactions promoted by trivalent tertiary phosphines

The background and recent breakthroughs in the single-electron-transfer (SET) reactions with trivalent tertiary phosphines are summarized and discussed in detail, and an outlook in the developments within this field is provided.

Nitrosobenzene: Reagent for the Mitsunobu Esterification Reaction

Nitrosobenzene has been demonstrated to participate in the Mitsunobu reaction in an analogous manner to dialkyl azodicarboxylates. The protocol using nitrosobenzene and triphenylphosphine (1:1) under mild conditions (0 °C) provides the ester derivatives of aliphatic and aromatic acids using various alcohols in moderate yield and with good enantioselectivity, giving the desired products predominantly with an inversion of configuration. The proposed mechanism, which is analogous to that observed using dialkyl azodicarboxylates, involves a nitrosobenzene-triphenylphosphine adduct and an alkoxytriphenylphosphonium ion and was supported by density functional theory calculations, ³¹P NMR spectroscopy, and experiments conducted with isotopically labeled substrates.

The catalytic Mitsunobu reaction: a critical analysis of the current state-of-the-art

The Mitsunobu reaction is widely regarded as the pre-eminent method for performing nucleophilic substitutions of alcohols with inversion of configuration. However, its applicability to large-scale synthesis is undermined by the fact that alcohol activation occurs at the expense of two stoichiometric reagents - a phosphine and an azodicarboxylate. The ideal Mitsunobu reaction would be sub-stoichiometric in the phosphine and azodicarboxylate species and employ innocuous terminal oxidants and reductants to achieve recycling. This Review article provides a summary and analysis of recent advances towards the development of such catalytic Mitsunobu reactions.

The Mitsunobu Reaction: Origin, Mechanism, Improvements, and Applications

The Mitsunobu reaction is a widely used and versatile method for the dehydrative oxidation-reduction condensation of an acid/pronucleophile usually with a primary or secondary alcohol that requires the combination of a reducing phosphine reagent together with an oxidizing azo reagent. The utility of this reaction stems from the fact that it is generally highly stereoselective and occurs with inversion of the stereochemical configuration of the alcohol starting material. Furthermore, as carboxylic acids, phenols, imides, sulfonamides, and other compounds can be used as the acid/pronucleophile, this reaction is useful for the preparation of a wide variety of functional groups. This Focus Review of the Mitsunobu reaction summarizes its origins, the current understanding of its mechanism, and recent improvements and applications.

Reaction of Diaryl-1,2-diones with Triphenylphosphine and Diethyl Azodicarboxylate Leading toN,N-Dicarboethoxy Monohydrazones via a Novel Rearrangement†

[reaction: see text]. A mechanistically novel reaction of diaryl-1,2-diones with diethyl azodicarboxylate and triphenylphosphine to afford N,N-dicarboethoxy monohydrazones is described. The reaction proceeds via a nitrogen to nitrogen migration of a carboethoxy group.

Mitsunobu Reaction of Unbiased Cyclic Allylic Alcohols

The stereochemical inversion of unbiased allylic alcohols using triphenylphosphine, diethyl azodicarboxylate, and benzoic acid, commonly known as the Mitsunobu reaction, was studied in three different solvents with specific attention toward the product composition. The results generated for the Mitsunobu reaction of (R)-3-deuterio-2-cyclohexen-1-ol and the cis and trans isomers of 1-deuterio-5-methyl-2-cyclohexen-1-ol, 1-deuterio-5-tert-butyl-2-cyclohexen-1-ol, and optically active cis and trans 5-isopropyl-2-methyl-2-cyclohexen-1-ol all gave similar product distributions with respect to inversion and retention at the carbinol center as well-as syn and anti S(N)2' type addition when THF or benzene was used as the solvent (CH(2)Cl(2) gave less selective product distributions). Interestingly, it was found that the quasi-equatorial and quasi-axial nature of the starting allylic alcohol does not appear to affect the product distribution for this reaction, nor does methyl substitution at the central carbon of the allylic alcohol. In all cases, significant amounts (8-28%) of non-S(N)2 type products were detected for these sterically unbiased allylic alcohols; only 72-77% of the product was from S(N)2 type reaction when sterically undemanding (R)-3-deuterio-2-cyclohexen-1-ol was subjected to Mitsunobu conditions.