B-alkyl suzuki-miyaura cross-coupling reactions with air-stable potassium alkyltrifluoroborates.

The palladium-catalyzed cross-coupling reaction of substituted potassium alkyltrifluoroborates with aryl halides and aryl triflates proceeds readily with moderate to good yields. The potassium alkyltrifluoroborates 1, 2, and 3a-e were easily synthesized and obtained as air-stable crystalline solids that can be stored for long periods of time. All of the cross-couplings proceed under the same reaction conditions using PdCl(2)(dppf).

Palladium-catalyzed Suzuki-Miyaura cross-coupling reactions of potassium aryl- and heteroaryltrifluoroborates.

An extended study of the reactivity of potassium aryl- and heteroaryltrifluoroborates in Suzuki-Miyaura cross-coupling reactions is presented. The coupling of aryl- and electron-rich heteroaryltrifluoroborates with aryl and activated heteroaryl bromides proceeds readily under ligandless conditions. When deactivated aryl- and heteroaryltrifluoroborates are coupled with aryl and heteroaryl bromides and chlorides, a low loading (0.

Suzuki-Miyaura cross-coupling reactions of potassium alkenyltrifluoroborates.

We have previously reported that the palladium-catalyzed cross-coupling reaction of air-stable potassium alkenyltrifluoroborates with aryl halides and triflates proceeds readily with good yields. Recent progress in outlining the scope and limitations of such reactions is described herein. The palladium-catalyzed cross-coupling reaction of potassium alkenyltrifluoroborates with aryl and heteroaryl halides and triflates proceeds readily with moderate to excellent yields.

Development of the suzuki-miyaura cross-coupling reaction: use of air-stable potassium alkynyltrifluoroborates in aryl alkynylations.

The palladium-catalyzed cross-coupling reaction of potassium alkynyltrifluoroborates with aryl halides or triflates proceeds readily with moderate to excellent yields. The potassium alkynyltrifluoroborates are air- and moisture-stable crystalline solids that can be stored indefinitely, which will provide an advantage in applications to combinatorial chemistry. The alkynyl cross-coupling reaction can be effected using 9 mol % of PdCl2(dppf).

Palladium-catalyzed cross-alkynylation of aryl bromides by sodium tetraalkynylaluminates.

Sodium tetraalkynylaluminates (1-4), prepared from NaAlH4 and terminal alkynes, cross-couple with aryl bromides in the presence of Pd(0) and Pd(II) catalysts. The reactions take place in boiling THF or DME. The process is applicable to both homo- and heterocyclic aryl bromides and can be used for conversion of polybromo compounds into polyalkynes.

Samarium(II) iodide-mediated intramolecular conjugate additions of alpha,beta-unsaturated lactones.

Samarium(II) iodide, in the presence of catalytic amounts of nickel(II) iodide, has been used to promote intramolecular conjugate additions of alkyl halides onto alpha,beta-unsaturated lactones. This process has been shown to be applicable to a number of alpha,beta-unsaturated lactones, including tetrasubstituted olefins, and has been demonstrated to be quite general for the formation of saturated bicyclic and tricyclic lactones. The method presented herein provides a mild, efficient process to form structurally complex lactones from simple precursors.

Efficient ligandless palladium-catalyzed Suzuki reactions of potassium aryltrifluoroborates.

[reaction: see text] The ligandless palladium-catalyzed Suzuki cross-coupling reaction of potassium aryl- and heteroaryltrifluoroborates with aryl- or heteroaryl halides or triflates proceeds readily with very good yields. The cross coupling can be effected in methanol or water, in the open air, using Pd(OAc)(2) as a catalyst in the presence of K(2)CO(3). A variety of functional groups are tolerated.

Sequenced reactions with samarium(II) iodide. Sequential intramolecular Reformatsky/nucleophilic acyl substitution reactions for the synthesis of medium-sized carbocycles.

Samarium(II) iodide was used to access eight- and nine-membered carbocycles via a domino reaction comprised of a Reformatsky reaction followed by a nucleophilic acyl substitution reaction. This method represents a general and efficient approach to a variety of highly functionalized, stereodefined carbocycles.

Suzuki cross-coupling reactions of potassium alkenyltrifluoroborates.

[reaction: see text] The palladium-catalyzed coupling reaction of potassium alkenyltrifluoroborates with aryl or alkenyl halides or triflates proceeds readily with good yields. The trifluoroborates are air- and moisture-stable solids that can be stored indefinitely. The cross-coupling can be effected using PdCl(2)(dppf).

Relative Rates of Hydrosilylation of Representative Alkenes and Alkynes by Cp(2)YMe.THF and [Cp(TMS)(2)YMe](2).

Reactivity in the hydrosilylation of alkenes and alkynes catalyzed by the organoyttrium catalysts Cp(2)YMe.THF and [Cp(TMS)(2)YMe](2) is generally determined by the steric environment of the substrate. Alkynes and conjugated alkenes show an increased reaction rate because of electronic effects; the magnitude of this increase is highly substrate dependent.

Sequential Ketyl-Olefin Coupling/beta-Elimination Reactions Mediated by Samarium(II) Iodide.

Samarium(II) iodide (SmI(2)) has been employed in an intramolecular sequential ketyl-olefin coupling/beta-elimination reaction. The overall process results in the net addition of an alkenyl species to a ketone carbonyl. This novel protocol for the intramolecular delivery of an alkenyl moiety avoids the basic reaction conditions typical of nucleophilic additions that are mediated by alkenylmagnesium halides and alkenyllithium reagents.

Conjugate Addition Reactions Mediated by Samarium(II) Iodide.

Samarium(II) iodide in conjunction with a catalytic low-valent transition metal species has been employed to promote the conjugate addition reaction of primary and secondary alkyl halides onto alpha,beta-unsaturated esters and amides. The method has been determined to be quite general and hence has been extended to the cyclization reactions of alkyl halides onto alpha,beta-unsaturated lactones, lactams, and nitriles. The cyclization reactions described herein provide a very general approach to the synthesis of functionalized carbocycles from simple acyclic precursors with excellent diastereoselectivity and under very mild reaction conditions.

Toward the total synthesis of variecolin.

[reaction: see text] An annulative approach toward the total synthesis of the sesterterpenoid variecolin (1) is presented. Synthesis of the key hemiketal, containing the core ABC ring skeleton, has been achieved on a model system by an expeditious route utilizing samarium(II) iodide. Furthermore, enantioselective syntheses of component fragments for the total synthesis have been developed.

Cross-coupling reactions of potassium alkyltrifluoroborates with aryl and 1-alkenyl trifluoromethanesulfonates.

[figure: see text] The palladium-catalyzed coupling reaction of potassium alkyltrifluoroborates with aryl- or alkenyltriflates proceeds to afford the corresponding arenes or alkenes in high yield. The borates are all solids, stable in air, and thus can be stored on the shelf indefinitely. The cross coupling can be effected using PdCl2(dppf).

Organolanthanide-catalyzed cyclization/boration of 1,5- and 1,6-Dienes.

[figure: see text] 1,5- and 1,6-Dienes undergo a cyclization/boration reaction in the presence of a catalytic amount of Cp*2Sm.THF. The resulting organoboranes can be oxidized to the corresponding primary cyclic alcohols using standard conditions.

Sequenced reactions with samarium(II) iodide. Sequential intramolecular Barbier cyclization/Grob fragmentation for the synthesis of medium-sized carbocycles.

Samarium(II) iodide was used to access eight-, nine-, and ten-membered carbocycles via a domino reaction composed of a cyclization/fragmentation process. 2-(Iodoalkyl)-, 2-(iodomethyl)allyl-, and 2-(2-iodomethyl)benzyl-2-methyl-3-(methanesulfonyloxy)cycloalkanones were subjected to Barbier-type reductive coupling conditions. Intermediate cycloalkanedione derivatives were also treated under similar conditions, providing bicyclic hydroxy ketones with complete diastereoselectivity and high yields.

A diastereoselective intramolecular hydroamination approach to the syntheses of (+)-, (+/-)-, and (-)-pinidinol.

A diastereoselective, lanthanocene-catalyzed, intramolecular hydroamination reaction was applied to the preparation of 2,6-disubstituted piperidines. Various metal/ligand arrays in the catalysts were examined using a model substrate to allow optimization of the diastereoselectivity. It was determined that the relationship between metal size and ligand bulk plays an integral role in the transformation.

Development of a protocol for eight- and nine-membered ring synthesis in the annulation of sp(2),sp(3)-hybridized organic dihalides with keto esters.

A protocol has been developed in which annulation reactions of various dihalides with keto esters can be carried out to provide entry to eight- and nine-membered carbocycles. In this process wherein one alkenyl- or aryl bromide and a tethered alkyl chloride comprise the organic dihalide, a selective metal-halogen exchange reaction between the sp(2)-hybridized bromide and an organolithium initiates the process. Transmetalation to an organoytterbium reagent generates a species that undergoes selective carbonyl addition to the ketone of the keto ester, creating a lactone intermediate.

Organoyttrium-catalyzed sequential Cyclization/Silylation reactions of nitrogen-heteroaromatic dienes demonstrating "Aryl-Directed" regioselectivity.

The reaction of 1-allyl-2-vinyl-1H-pyrroles and 1-allyl-2-vinyl-1H-indoles with arylsilanes in the presence of catalytic [Cp(TMS)(2)Y(&mgr;-Me)](2) leads to highly selective cyclization/silylation events. In this process the active catalyst for the reaction, "Cp(TMS)(2)YH", undergoes initial olefin insertion at the vinyl group. Even isopropenyl substituents on the heteroaromatics react in preference to less sterically encumbered allyl groups.

Hemidesmosomal molecular changes in dermatitis herpetiformis; decreased expression of BP230 and plectin/HD1 in uninvolved skin.

Recent BP230-knockout experiments with subsequent blistering and recently identified plectin/HD1 mutations in epidermolysis bullosa simplex patients suggest that defective expression of BP230 and plectin/HD1 may predispose to blister formation in human skin. We have studied the expression of the epithelial adhesion complex as well as the basement membrane and anchoring fibril antigens in uninvolved dermatitis herpetiformis skin to find out if alterations can be detected in these structures predisposing to the blister formation typical of the disease. Ten uninvolved dermatitis herpetiformis skin specimens, which all showed clear granular deposits of IgA under the basement membrane in direct immunofluorescence and five normal skin specimens, were studied by indirect immunofluorescence technique.

Total Synthesis of (-)-Cylindricine C.

(-)-Cylindricine C has been synthesized from commercially available ()-(-)-1,2,4-butanetriol in 11 steps with an overall yield of 12%. The key step utilizes a CrCl reduction of an azide to form the corresponding amine with a subsequent double Michael addition to create the tricyclic skeleton of cylindricine from a monocyclic substrate.

Sequenced Reactions with Samarium(II) Iodide. Sequential Nucleophilic Acyl Substitution/Ketyl Olefin Coupling Reactions for the Preparation of Oxygen Heterocycles.

Samarium(II) iodide has been employed to promote a sequential intramolecular nucleophilic acyl substitution/intramolecular ketyl olefin coupling cyclization sequence to provide bicyclic, tricyclic, and spiro-fused oxygen heterocycles in excellent yield and with high diastereoselectivity.