A stereoselective palladium-catalyzed oxidative carbocyclization/arylation of enallenes is described. The reaction shows wide tolerance toward highly functionalized arylboronic acids and results In a cis addition of two carbon moieties to an olefin in good to excellent yields.

A highly selective oxidative palladium(II)-catalyzed (Wacker-type) cyclization of readily available allylic tosylcarbamates is reported. This operationally simple catalytic reaction furnishes tosyl-protected vinyl-oxazolidinones, common precursors to syn-1,2-amino alcohols, in high yield and excellent diasteroselectivity (>20:1). It is demonstrated that both stoichiometric amounts of benzoquinone (BQ) as well as aerobic reoxidation (molecular oxygen) is suitable for this transformation. The title reaction is shown to proceed through overall trans-amidopalladation of the olefin followed by beta-hydride elimination. This process is scalable and the products are suitable for a range of subsequent transformations such as: kinetic resolution (KR) and oxidative Heck-, Wacker-, and metathesis reactions.

An efficient oxidative carbocyclization/borylation of enallenes uses Pd(OAc)₂ as the catalyst, B₂pin₂ as the boron-transfer reagent, and 1,4-benzoquinone (BQ) as the oxidant (see scheme). The reaction seems to take place through activation of the allene by a Pd^II complex to give an alkenyl–Pd^II intermediate followed by carbopalladation of the olefin and subsequent cleavage of the intermediate palladium–carbon bond by the boron reagent.

The main focus of this thesis has been directed towards preparation and oxidative carbocyclization of en-, dien- and aza-enallenes.

In the first part of this thesis, a stereoselective oxidative carbocyclization of dienallenes was realized. By employing cheap and readily available palladium trifluoroacetate we were able to efficiently cyclize a variety of dienallenes into hydroxylated carbocycles in high yield and high selectivity. This oxidative process was compatible with two different reoxidation protocols: one relying on p-benzoquinone (BQ) as the oxidant and the other employing molecular oxygen as the oxidant.

In the second part of the thesis the carbocyclization methodology was extended to include carbocyclization of aza-enallenes. This was achieved in two distinct steps. First, a copper-catalyzed coupling of allylic sulfonamides with bromoallenes was developed, giving access to the corresponding aza-enallenes. Subjecting these substrates to catalytic amounts of palladium acetate, along with BQ as the oxidant, rendered N-heterocycles in good yield. The reactivity of these N-heterocycles towards activated dienophiles was later exploited in a tandem (aerobic) oxidative carbocyclization/Diels-Alder reaction.

The third topic involves efficient oxidative arylative/borylative carbocyclization of enallenes. These reactions, catalyzed by palladium acetate, relies on transmetallation of a (σ-alkyl)palladium(II) intermediate with diboranes or arylboronic acids. With this novel methodology we were able to obtain an array of arylated or borylated carbocycles, as single diastereomers, in high yield.

Finally, we developed a palladium(II)-catalyzed cyclization of allylic carbamates. This mild, operationally simple, and scalable catalytic reaction opens up access to an array of oxazolidinones in high yield and excellent diastereoselectivity.

Live and let diene: A palladium(II)-catalyzed oxidative carbocyclization reaction of aza-enallenes provides access to potentially valuable heterocyclic dienes. In the presence of a dieneophile during the carbocyclization step, the products can react further in a one-pot cyclization/Diels–Alder sequence to give polycyclic products. BQ=para-benzoquinone

Allylic allenic amides have been synthesized via a copper-catalyzed cross-coupling between allylic sulfonamides and bromoallenes in moderate to good yields. Copper(I) thiophene-2-carboxylate (CuTC) was used a source of copper with DMEDA as the ligand. The allenylated products obtained are potential substrates for palladium-catalyzed carbocyclizations.

An efficient palladium(II)-catalyzed oxidative carbohydroxylation of allene-substituted conjugated dienes in aqueous media has been developed. The reaction is conducted employing p-benzoquinone as the stoichiometric reoxidant for the palladium or under aerobic conditions with essentially the same outcome. It is worth mentioning that this is the first example of a palladium(II)-catalyzed oxidation where a carbon−carbon bond is formed in water and also one of the few cases of nucleophilic attack by water on a (π-allyl)palladium complex.

An enantioselective method for the synthesis of α-methyl carboxylic acids starting from trans-cinnamaldehyde, a readily available and inexpensive compound, has been developed. Allylic alcohol 1 was obtained via a standard Grignard addition to trans-cinnamaldehyde. Dynamic kinetic resolution was applied to allylic alcohol 1 utilizing a ruthenium catalyst and either an (R)-selective lipase or an (S)-selective protease to provide the corresponding allylic esters in high yield and high ee. A copper-catalyzed allylic substitution was then applied to provide the corresponding alkenes with inversion of stereochemistry. Subsequent C−C double bond cleavage afforded pharmaceutically important α-methyl substituted carboxylic acids in high ee and overall yields of up to 76%.