Jack K. Crandall

Reductive cyclizations of allenic ketones by dissolving metals

Abstract The dissolving metal reductions of certain allenic carbonyl compounds leads to the formation of cyclic alcohols with high regioselectivity.

Siloxanes from the hydrolysis of isopropyltrimethoxysilane

Abstract The behavior of isopropyltrimethoxysilane (1 in the presence one equivalent of water and a dibutyltin dilaurate catalyst has been investigated. Under these conditions, partial hydrolysis of the methoxy groups of 1 occurred, followed by condensation reactions leading to the formation of low molecular-weight oligomers. Disiloxane 4, trisiloxane 6 and cyclic siloxane 7 and 8 have been isolated and fully characterized. Transient reaction intermediates silanol 3 and hydroxydisiloxane 5 have been characterized spectroscopically. The time evolution of these species was followed by gas chromatography and 29Si NMR. A reaction scheme for the hydrolytic condensation of 1 is proposed to accomodate these results.

The formation of orthoquinones in the dimethyldioxirane oxidation of phenols

Abstract The dimethyldioxirane oxidation of selected phenols provides the corresponding orthoquinones. This conversion proceeds via the related arenediols, which are cleanly oxidized to the quinones by this oxidant.

Allene Epoxidation. Highly functionalized tetrahydrofurans and tetrahydropyrans from the oxidative cyclization of allenic alcohols.

Abstract The dimethyldioxirane oxidation of various allenic alcohols yields highly functionalized tetrahydrofuran and tetrahydropyran derivatives via intramolecular nucleophilic addition of the hydroxy group to an intermediate allene diepoxide.

Allene epoxidation: synthesis of functionalized lactones by the DMDO oxidation of allenic acids

Abstract A series of allenic carboxylic acids has been converted to functionalized lactones by oxidation–cyclization promoted by dimethyldioxirane. These transformations are rationalized by the involvement of unisolated allene oxide and spirodioxide intermediates. The structures of the starting allenic acids and the reaction conditions determine which of these two intermediate species serves as the source of the isolated products. The use of prepared solutions of the oxidant generally proceed via spirodioxides; whereas in situ reactions normally give products derived from the allene oxides. When products are formed directly from allene oxides, keto lactones are formed. The corresponding spirodioxide intermediates give lactones with appropriately situated α-hydroxyketone moieties. An understanding of the regiochemistry of the epoxidations and the subsequent cyclizations of the reactive intermediates is developed, as are methods for the manipulation of the experimental conditions to favor the desired products.

Oxidative cyclizations of allenic aldehydes

Abstract Allenyl aldehydes and ketones are oxidatively cyclized by dimethyldioxirane to provide cyclic acetals and hemiacetals.

Radical cyclizations of functionalized allenes

Abstract Substitution of P(O)Ph 2 , SOPh, and SO 2 Ph on an allene facilitates intramolecular radical addition to the central allene carbon to provide good yields of five-, six-, and seven-membered carbocycles.

Oxidative cyclizations of allenic sulfonamides with dimethyldioxirane

Abstract The dimethyldioxirane oxidations of allenic amine derivatives give highly functionalized nitrogen heterocycles derived from cyclizations of intermediate allene mono- and diepoxides.

Allene epoxidation. Oxidative cyclizations of allenyl alcohols.1

Abstract The dimethyldioxirane oxidation of various allenic alcohols yields highly functionalized tetrahydrofuran and tetrahydropyran derivatives via intramolecular nucleophilic addition of the hydroxy group to an intermediate allene diepoxide.

ALLENE EPOXIDATION. OXIDATIVE CYCLIZATIONS OF ALLENYL ACIDS

The dimethyldioxirane oxidation of a series of allenyl carboxylic acids with varying numbers (0-3) of carbons between the two functions leads to highly functionalized lactones derived from cyclization of intermediate diepoxides. The regiochemistry is generally controlled so as to give γ- and δ-lactones