The versatility of alpha-chloropropargyl phenyl sulfide affords high stereo- and regioselectivities in indium-promoted coupling reactions under mild conditions.

Coupling reactions between alpha-chloropropargyl phenyl sulfide (11) and a series of aldehydes under aqueous conditions are reported. Not only is good stereoselectivity observed between syn and anti isomeric products, but excellent regioselectivity is also witnessed. In reactions using indium metal as a promoter, the propargyl functionality (12) is retained, unlike the use of more traditional metals that result in formation of products containing a mixture of both propargyl (12) and allene (13) moieties. The reaction is postulated to proceed via either a chelated or nonchelated route, controlled by the presence or absence of indium (III) chloride, and may be used to create synthetically useful building blocks. The formation of epoxyalkyne (14) molecules, which are found in many natural products and have wide use as synthetic templates, is presented as one example.

Diastereoselection during 1,2-Addition of the Allylindium Reagent to alpha-Thia and alpha-Amino Aldehydes in Aqueous and Organic Solvents.

The stereochemistry of the indium-promoted reaction of allyl bromide with alpha-thia (PhS and MeS), disubstituted alpha-amino (Bn(2)N, Me(2)N, isoindolyl), and protected alpha-amino aldehydes (Ac and Boc) in water has been evaluated. The reactions involving the sulfur derivatives are minimally diastereoselective, indicating that the allylindium reagent is not thiophilic. Chelation is not observed and pi-facial discrimination is achieved via Felkin-Ahn transition states under the steric control of the substituents. The Garner aldehyde is also anti-diastereoselective. Interestingly, N-acetylmannosamine is appreciably responsive to chelation control and is capable of generating 90% of the syn beta-amino alcohol when reacted in a 0.5 M NH(4)Cl solution. While the alpha-dibenzylamino substituent is too bulky to enter into complexation, the alpha-dimethylamino group is not and can lead to high levels (99%) of syn diastereomer. The size of other neighboring substituents does have an impact on pi-facial discrimination in these systems and can erode the stereoselectivity accordingly.

Comparative Diastereoselectivity Analysis of Crotylindium and 3-Bromoallylindium Additions to alpha-Oxy Aldehydes in Aqueous and Nonaqueous Solvent Systems.

The couplings of crotyl bromide (1) and 1,3-dibromopropene (2) to a triad of conformationally unrestricted alpha-oxy aldehydes in water, aqueous THF (1:1), and anhydrous THF are described. In no example involving 1 was the formation of anti,syn product detected. The proportion of syn isomers reached a maximum (syn/anti = 5.6:1) when the neighboring hydroxyl group was unprotected and water was the reaction medium. Although internal chelation also operates to some degree with 2, considerable erosion of this mechanistic pathway (maximum now only 2:1) in favor of Felkin and "anti-Felkin" transition states is reflected in the product distributions. This trend can be synthetically advantageous, and a utilitarian example is demonstrated. The indium reagents studied here are notably efficient nucleophilic reaction partners in water.