Alpha rules: A thiourea acts as an efficient organocatalyst for the glycosylation of protected galactals to form oligosaccharides containing a 2-deoxymonosaccharide moiety. The reaction is highly stereoselective for α-linkages and proceeds by way of a syn-addition mechanism.

The asymmetric allylation and crotylation of aromatic aldehydes with allylic trichlorosilanes can be promoted by chiral phosphoramides in high yield and modest enantiomeric excess. The reaction likely proceeds via a hexacoordinate siliconate species.The asymmetric addition of allylmetal reagents to aldehydes has evolved into a powerfiil and selective tactic in modem organic synthesis.1 Among the most common strategies to accomplish asymmetric allylation is the use of reagents in which the metal is ligated by chiral modifiers. This approach has been extensively developed with excellent results for boron* 12 and titanium,3 but with more modest results for silicon4 5and tin.5,6 The reason for this dichotomy rests squarely in the mechanistic differences in these transformations; i.e., allylboranes and titanium reagents are type l7 reagents which react through associative cyclic transition structures while allylsilanes and -stannanes are type 2 reagents which react (under Lewis acid catalysis) through less rigid, open transition structures.8Recently, a number of laboratories have recorded a significant advance in asymmetric additions of allyl-silanes9 and -stannanes10 *by the use of chiral Lewis acid

A practical approach has been developed to convert glucals and rhamnals into disaccharides or glycoconjugates with high α-selectivity and yields (77–97 %) using a trans-fused cyclic 3,4-O-disiloxane protecting group and TsOH⋅H2O (1 mol %) as a catalyst. Control of the anomeric selectivity arises from conformational locking of the intermediate oxacarbenium cation. Glucals outperform rhamnals because the C6 side-chain conformation augments the selectivity.

A series of saligenin beta(2) adrenoceptor agonist antedrugs having high clearance were prepared by reacting a protected saligenin oxazolidinone with protected hydroxyethoxyalkoxyalkyl bromides, followed by removal of the hydroxy-protecting group, alkylation, and final deprotection. The compounds were screened for beta(2), beta(1), and beta(3) agonist activity in CHO cells. The onset and duration of action in vitro of selected compounds were assessed on isolated superfused guinea pig trachea. Compound 13f had high potency, selectivity, fast onset, and long duration of action in vitro and was found to have long duration in vivo, low oral bioavailability in the rat, and to be rapidly metabolized. Crystalline salts of 13f (vilanterol) were identified that had suitable properties for inhaled administration. A proposed binding mode for 13f to the beta(2)-receptor is presented.

O(Silacyclobuty1) ketene acetals derived from esters, thiol esters, and amides underwent facile aldol addition with a variety of aldehydes at room temperature without the need for catalysts. The uncatalyzed aldol addition reaction of O(silacyclobuty1) ketene acetals displayed the following characteristics: (1) the rate of reaction was highly dependent on the spectator substituent on silicon and the geometry of the ketene acetal, (2) the 0,O-ketene acetal of E configuration afforded the syn aldol products with high diastereoselectivity (93/7 to 99/1), (3) conjugated aldehydes reacted more rapidly than aliphatic aldehydes, and (4) the reaction was mildly sensitive to solvent. In addition, the aldol reaction was found to be efficiently catalyzed by metal alkoxides. Labeling experiments revealed that the thermal aldol reaction proceeds by direct intramolecular silicon group transfer, while the alkoxide-catalyzed version probably proceeds via in situ generated metal enolates. Computational modeling of the transition states suggests that the boat transition structures are preferred, supporting the observed syn selectivity of the thermal aldol reaction. Both thermal and alkoxide-catalyzed Michael additions were investigated, revealing a competition between 1,2-and 1 ,Caddition favoring the former.