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The reactions of dialkylzinc reagents with ketones are scarcely studied. In this paper, we describe a previously unknown direct alkylation of substituted 2-acetylpyridine with diisopropyl zinc, which gave a corresponding novel alcohol with 82% yield. [ABSTRACT FROM AUTHOR]

A case of spontaneous chirality generation was observed during a synthetic project studying the allylboration of 1,2,3-triazolic aldehydes. Here, we present computational studies supported by experimental findings targeting the elucidation of border conditions required for the observation of spontaneous chirality generation in the reaction of 1-Ar-1H-1,2,3-triazole-4-carbaldehydes 1a,b with triallylborane. Three possible sources of symmetry breaking were found computationally. Thus, dimerization of the initial reaction products, alcoholates 4a,b, gives dimers 5a,b (homochiral) and 6a,b (heterochiral). The latter were computed to be more stable thermodynamically, which can lead to amplification of the initial stochastic imbalance of the enantiomers of 4a,b via the reservoir mechanism. Furthermore, enantiomeric excess can be increased during the transfer of the second allylic group in the reaction of optically active boronates 4a,b with 1a,b, which was computed to be enantioselective due to the strong activating and stereoregulating properties of the 1,2,3-triazole group. In addition, reactions of borinic esters 8a,b, products of the previous reaction with triallylborane, recovered in each case two molecules of 4a,b of the same handedness, which can lead to additional chirality amplification. Experimentally, reactions of optically active alcohols (+)-R-2a,b with triallylborane provided chiral alcoholates 4a,b, which were reacted with equivalent amounts of corresponding aldehydes 1a,b. Unexpectedly, in two series of 10 experiments each, preferential formation of both enantiomers of the newly formed product was observed: seven times S and three times R in the case of 1a and six times S and four times R in the case of 1b. [ABSTRACT FROM AUTHOR]

A previously unknown reduction of carbonyl compounds with dicyclopentylzinc is reported. Aldehydes react in mild conditions yielding corresponding primary alcohols and cyclopentene. Although cyclohexanone and acetophenone are inert to dicyclopentylzinc, a variety of heterocyclic ketones reacted readily, yielding reasonable to high yields of corresponding secondary alcohols. When the reaction was catalyzed with (–)-(1R,2S)-ephedrine, 3-acetylpyridine (10) resulted in a high yield of (S)-1-(pyridin-3-yl)ethanol (19) with >99% ee. 5-Acetyl-2-bromopyridine (11) also provided the corresponding optically active alcohol 20, albeit with a much lower optical yield. When 10% of 19 with 92% ee was used as an autocatalyst, 55% yield of the same compound was obtained, with 95% ee and 96% ee in two independent experiments. A three-stage reaction sequence starting from "no chirality" reaction yielded 19 with 6% ee. Thus, amplifying autocatalysis was detected in the reaction of ketone 10 with dicylopentylzinc. [ABSTRACT FROM AUTHOR]

The phenomenon of amplifying asymmetric autocatalysis (AAA) has recently been restricted to alkylation of several specific substrates with diisopropyl zinc (Soai reaction). Targeting the extension of the scope of this phenomenon, we studied the reaction of triazolic aldehydes with diisopropyl zinc. Experiments demonstrated a diversity of results for the dissipation of chirality, conserving the existent ee and spontaneous chirality generation. Computational analysis showed that depending on the level of oligomerization of the catalyst, one could expect amplification (monomeric catalyst) while maintaining the existing chirality (dimeric catalyst) or dissipation of chirality (tetrameric catalyst). These findings are promising for the elaboration of synthetic protocols controlling chirality generation. In addition, three optically active triazolic alcohols were characterized. [ABSTRACT FROM AUTHOR]

Global reaction route mapping (GRRM) analysis for compounds with the formula C4H5NO allowed for the detection of the corresponding "Guinness molecules" 000 and 001, as well as around 150 other stable minima of the same composition. The results suggest that compounds of similar functionality form a kind of "Stability Island" with their free energies of formation falling within s relatively limited range. [ABSTRACT FROM AUTHOR]

The mechanism of asymmetric hydrogenation catalyzed by an Rh-complex of (R)-(tert-butylmethylphosphino)(di-tert-butylphosphino)methane is examined. The different reactivities of diastereromeric catalyst-substrate complexes and a new approach are described for rationalizing the enantioselection in Rh-catalyzed asymmetric hydrogenation.

A novel approach for asymmetric intramolecular hydroamination, hydroalkoxylation and hydrocarbonation of alkynes using chiral palladium catalysts are described. It was found that a chiral palladium catalyst, derived from [Pd.sub.2][(dba).sub.3].CH[CI.sub.3] and (R,R)-renorphos is highly effective for catalyzing asymmetric intramolecular hydroamination.

Optically active 1,2-bis(alkylmethylphosphino)ethanes and bis(alkylmethylphosphino)methanes are unique diphosphine ligands combining the simple molecular structure and P-stereogenic asymmetric environment. This work shows that these ligands exhibit excellent enantioselectivity in rhodium-catalyzed asymmetric hydrogenation of [alpha],[beta]-unsaturated phosphonic acid derivatives. The enantioselective hydrogenation mechanism elucidated by NMR study is also described.

Research into the scope and limitations of the asymmetric hydrogenation of enamides catalyzed by the rhodium complexes of t-Bu-BisP* and t-Bu-Mini-PHOS is presented. The t-Bu-BisP*-Rh catalyst was found to be one of the best catalysts for the asymmetric hydrogenation of enamides identified so far.

Research was conducted to examine the behavior of 9-cyclopentyl-09-borabarbaralane following reactions with acetic acid, ethoxyacetylene, acetonitrile, acetaldehyde and acetone. Results show that the reactions produced products similar to the derivatives of 9-cyclopentyl-9-borabicyclo[4.2.1]nona-2,4,7-triene. In addition, boronic ester was formed following methanolysis of 9-cyclopentyl-09-borabarbaralane.

The synthesis and dynamic properties of cycloheptatrienyl(dipropyl)borane was determined through the exchange reaction of trimethyl(cycloheltatrienyl)tin and dipropylchloroborane and nuclear magnetic resonance spectroscopy. Ab initio calculations demonstrate that the donor-acceptor interaction between the Walsh orbital of the cyclopropane and the boron 2p AO is effective in the exo-norcaradiene form. Results also suggest that the boron 2p AO is necessary for the stabilization of the norcaradiene form.

The synthesis of endo-2-pivaloyl-endo-8-hydroxybicyclo(3.3.0)octane is described. The method involves the acylation of (Z,Z)-1,5-cyclooctadiene with pivaloyl tetrafluoroborate at -78 degrees Centigrade. The reaction mixture was stored at room temperature and then refluxed at 42 degrees Centigrade for 36 hours before hydrolysis. The reaction mechanism for the synthesis is presented.

A new transformation pattern for enantioselective intramolecular hydroacylation has been developed involving an alkene isomerization strategy. Proceeding through a five‐membered rhodacycle intermediate, 3‐enals were converted to C3‐ or C3,C5‐chirogenic cyclopentanones with satisfactory yields, diastereoselectivities, and enantioselectivities. A catalytic cycle has been theoretically calculated and the origin of the stereoselection is rationally explained. [ABSTRACT FROM AUTHOR]