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[reaction: see text] Treatment of O-homoallylhydroxylamines with palladium(II) and copper(II) in the presence of a base, methanol, and carbon monoxide results in the formation of isooxazolidines. An electron-withdrawing group on the hydroxylamine nitrogen is essential. When carbamate groups are used the products are formed exclusively as their cis isomers.

The catalytic, diastereoselective coupling of α-silyloxy aldehydes and alkynylsilanes catalyzed by a nickel(0) N-heterocyclic carbene complex provides an effective entry to anti-1,2-diols. The scope of couplings and extent of diastereoselection are excellent across a range of substrates.Diastereoselective nucleophilic additions to α-alkoxy aldehydes provide an attractive method for preparation of 1,2-diols. Synthesis of anti-1,2-diols can be achieved by additions to chiral aldehydes following the Felkin model for diastereoselection, although control of stereochemistry can often be a challenge. A number of studies involving alkenylation of α-alkoxy aldehydes illustrate that anti selectivity can sometimes be achieved, but that the results are variable depending upon the precise structure of both the chiral aldehyde and vinyl organometallic. 1,2 Several attractive alternative strategies that rely upon aldol technology have also been developed to avoid these limitations. 3 The nickel-catalyzed addition of aldehydes and alkynes has emerged as a useful way to prepare allylic alcohols in a variety of contexts. 4,5 Several reports of nickel-catalyzed reductive couplings of this class involving highly stereoselective additions to chiral α-alkoxy aldehydes have appeared. 6,7 Absent among the reports involving nickel catalysis is the intermolecular diastereoselective addition of non-aromatic alkynes, terminal alkynes, and silyl alkynes. Additionally, intermolecular additions involving α-alkoxyaldehydes bearing an unbranched substituent at the α-carbon proceeded with modest diastereoselectivity. 6c Given the utility of catalytic couplings of aldehydes and alkynes involving nickel(0) / N-heterocyclic carbene catalysts recently disclosed from our group, 8 we have examined this catalyst formulation in diastereoselective additions of alkynes to α-silyloxyaldehydes. The reaction scope and extent E-mail: jmontg@umich.edu. Although our group previously demonstrated that the structure of an N-heterocyclic carbene ligand can play an important role in determining yield and regioselectivity in nickel-catalyzed aldehyde / alkyne reductive couplings, the current study focused exclusively on reactions involving Ni(COD) 2 and the N-heterocyclic carbene (IMes) derived from imidazolium 1 in THF. From our prior studies, we recognized that silane structure was important in order to select for the desired three component coupling over undesired hydrosilylation of the aldehyde or alkyne moieties. We thus compared the catalytic addition of a TBS-protected silyloxy aldehyde with trimethylsilyl(phenyl)acetylene using various silanes. Due to competing hydrosilylation processes with unhindered silanes, chemical yields with (i-pr) 3 SiH were superior to (t-Bu)Me 2 SiH and Et 3 SiH (Table 1, entries 1-3). We next compared (i-pr) 3 SiHmediated couplings of TMS-propyne with various α-oxyaldehydes (Table 1, entries 4-7). Both diastereoselectivities and yields were only modestly impacted in comparing α-benzyloxy to various α-silyloxy groups, ...

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