William F. Bailey

Synthesis of heterocycles by cyclization of unsaturated organolithiums: a review

The preparation of oxygen and nitrogen containing heterocyclic compounds by cyclization of unsaturated organolithium compounds has been reviewed. The review contains 57 references to relevant literature through early 2001.

Oxidative cleavage of benzylic and related ethers, using an oxoammonium salt.

Benzylic ethers and related ArCH(2)OR substrates are oxidatively cleaved by 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (1) in wet CH(3)CN at room temperature to give the corresponding aromatic aldehyde and alcohol in high yield. Primary or secondary alcohol products are further oxidized by 1 to give carboxylic acids and ketones, respectively. The oxidation likely involves a formal hydride abstraction from the benzylic carbon as evidenced by slow reaction of substrates bearing electron-withdrawing substituents.

Metal-halogen interchange between t-butyllithium and 1-iodo-5-hexenes provides no evidence for single-electron transfer

Abstract No products attributable to cyclization of 5-hexen-1-yl radicals have been detected in reactions of t -butyllithium with 1-iodo-5-hexenes at −78°C. Such experiments provide no evidence for the intermediacy of free-radicals in the metal—halogen interchange of primary alkyliodides with t -C4H9Li.

Access to Nitriles from Aldehydes Mediated by an Oxoammonium Salt

A scalable, high yielding, rapid route to access an array of nitriles from aldehydes mediated by an oxoammonium salt (4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate) and hexamethyldisilazane (HMDS) as an ammonia surrogate has been developed. The reaction likely involves two distinct chemical transformations: reversible silyl-imine formation between HMDS and an aldehyde, followed by oxidation mediated by the oxoammonium salt and desilylation to furnish a nitrile. The spent oxidant can be easily recovered and used to regenerate the oxoammonium salt oxidant.

Intramolecular addition of alkyllithiums to acetylenes: Regiospecific 4-, 5-, and 6-exo-dig cyclizations

Abstract Primary acetylenic alkyllithiums bearing a phenyl substituent on the triple bond, which may be prepared in virtually quantitative yield by low-temperature lithium-iodine interchange, undergo regiospecific exo-dig cyclization via stereoselective syn-addition of CH 2 Li to the carbon-carbon triple bond to give four-, five-, and six-membered carbocycles bearing an easily functionalized exocyclic lithiomethylidene moiety. Cyclization of the analogous alkyl substituted acetylenic alkyllithiums is confined to the 5- exo-dig mode.

Preparation and facile cyclization of 5-alkyn-1-yllithiums

Abstract Primary 5-hexyn-1-yllithiums, which may be generated in virtually quantitative yield by low-temperature lithium-iodine interchange, undergo regiospecific 5-exo-dig cyclization via stereoselectively syn-addition of CH 2 Li to the alkyne moiety to give vinyllithiums that may be trapped with any of a variety of electrophiles to deliver functionalized cyclopentylidene- containing products.

Selective oxoammonium salt oxidations of alcohols to aldehydes and aldehydes to carboxylic acids.

The oxidation of alcohols to aldehydes using stoichiometric 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (1) in CH(2)Cl(2) at room temperature is a highly selective process favoring reaction at the carbinol center best able to accommodate a positive charge. The oxidation of aldehydes to carboxylic acids by 1 in wet acetonitrile is also selective; the rate of the process correlates with the concentration of aldehyde hydrate. A convenient and high yield method for oxidation of alcohols directly to carboxylic acids has been developed.

Anionic cyclization of olefinic alkyllithiums: ring closure of terminally substituted 5-hexenyllithiums.

Abstract A series of 5-hexenyllithiums having a phenyl, trimethylsilyl, or cyclopropyl substituent at the terminal [C(6)] alkene carbon have been prepared from the corresponding iodides by lithium-iodine exchange with t-butyllithium at −78 °C. Although 6-alkyl-substituted 5-hexenyllithiums do not isomerize to five-membered rings upon warming, terminally substituted 5-hexenyllithiums bearing a moderately activating phenyl or trimethylsilyl group cleanly undergo a totally regiospecific 5-exo cyclization at sub-ambient temperatures to afford five membered rings bearing a CHRLi moiety that may be trapped with an electrophile to deliver high yields of functionalized product. Cyclization of 6-cyclopropyl-5-hexenyllithium is accompanied by ring opening of the three-membered ring.

Bicyclo[2.2.0]hex-1(4)-ene

Abstract The preparation of bicyclo [2.2.0]hex- 1(4)-ene ( 1 ) via ring expansion of a cyclopropylcarbene or the dehalogenation of 1-bromo-4-chlorobicyclo[2.2.0]hexane is described. It is one of the most reactive of the alkenes which may be observed at room temperature. Its reactions, including dimerization and cycloaddition reactions, are described. The latter lead to convenient preparations of [m.2.2]propellanes. The vibrational spectrum was examined via matrix isolation and ab initia MO calculations.

Reactions of 1-halo-5-hexenes with alkyllithiums. Evidence for a pronounced halogen effect on the mechanism of the metal—halogen interchange reaction of primary alkyl halides

Abstract Reaction of t -BuLi with 1-halo-5-hexenes and 1-halo-6-methyl-5-heptenes at −78°C has revealed that, whereas 1° alkyl iodides are cleanly converted to alkyllithiums in a non-radical process, the corresponding 1° alkyl bromides undergo interchange at least partially via a radical-mediated, SET pathway.