A new chiral building block for the direct installation of the 1,3-diol motif is presented. Aldehyde olefination followed by directed reduction allows for the synthesis of both the syn- and the anti-configured diol in a fully stereocontrolled way. The building block was used for the total synthesis of naturally occurring 1,2,4-trihydroxynonadecanes starting from pentadecanal.

The acylation of alcohols catalyzed by N,N-dimethylamino pyridine (DMAP) is, despite its widespread use, sometimes confronted with substrate-specific problems: For example, target compounds with multiple hydroxy groups may show insufficient selectivity for one hydroxyl, and the resulting product mixtures are hardly separable. Here we describe a concept that aims at tailor-made catalysts for the site-specific acylation. To this end, we introduce a catalyst library where each entry is constructed by connecting a variable and readily tuned peptide scaffold with a catalytically active unit based on DMAP. For selected examples, we demonstrate how library screening leads to the identification of optimized catalysts, and the substrates of interest can be converted with a markedly enhanced site-selectivity compared with only DMAP. Furthermore, substrate-optimized catalysts of this type can be used to selectively convert “their” substrate in the presence of structurally similar compounds, an important requisite for reactions with mixtures of substances.

Phosphane and N-heterocyclic carbene ligated gold(I) chlorides can be effectively activated by Na[Me₃NB₁₂Cl₁₁] (1) under silver-free conditions. This activation method with a weakly coordinating closo-dodecaborate anion was shown to be suitable for a large variety of reactions known to be catalyzed by homogeneous gold species, ranging from carbocyclizations to heterocyclizations. Additionally, the capability of 1 in a previously unknown conversion of 5-silyloxy-1,6-allenynes was demonstrated.

The generation of highly substituted furans from propargyl vinyl ethers bearing a free hydroxy group was investigated. In the presence of catalytic amounts of AgBF₄, a formal [3,3] sigmatropic rearrangement takes place in the first stage of the sequence. The resulting allenyl carbonyl intermediates then undergo cyclocondensation, which upon double-bond isomerization leads directly to the five-membered heterocyclic products. This domino reaction allows the synthesis of various tri- and tetrasubstituted furan products; an example leading to pyrroles in an analogous way is also described.

A convenient method for the mild dehydrogenation of β-oxonitriles is presented. When treated with o-iodoxybenzoic acid (IBX), a range of these compounds were transformed into their unsaturated counterparts. Furthermore, we show that the products of the dehydrogenation can react in situ, undergoing rapid hetero-Diels–Alder reactions with enol ethers to give multiply substituted dihydropyrans. We also describe the dehydrogenation of cyclic β-oxonitriles, which leads to the formation of substituted phenols.

Three simple methods for the synthesis of geminal triazides are described: Starting from 1) 3-oxocarboxylic acids, 2) iodomethyl ketones, or 3) terminal olefins, a range of triazidomethyl ketones can be constructed under mild oxidative reaction conditions by the use of IBX-SO₃K, a sulfonylated derivative of 2-iodoxybenzoic acid (IBX), and NaN₃ as an azide source. This is the first report of representatives of this novel class of triazide compounds: Despite their high nitrogen content, the geminal triazides are easy to handle, even when preparative-scale syntheses are performed. (Caution: These procedures still require protective measures!) The triazides are now broadly available for further studies regarding their properties and reactivity. Furthermore, we show how the method can be used to provide α-azidoesters, which are potential building blocks for amino acids.

Drei einfache Methoden zur Synthese geminaler Triazide werden beschrieben: Ausgehend von 1) 3-Oxocarbonsäuren, 2) Iodmethylketonen oder 3) terminalen Olefinen gelingt der Aufbau einer Reihe von Triazidomethylketonen unter milden, oxidativen Reaktionsbedingungen mit IBX-SO₃K, einem sulfonierten Derivat der 2-Iodoxybenzoesäure (IBX), und NaN₃ als Azidquelle. Von dieser neuen Verbindungsklasse sind bislang keine Mitglieder beschrieben. Die geminalen Triazide erweisen sich trotz ihres hohen Stickstoffgehalts auch in präparativen Mengen als unerwartet leicht handhabbar (Vorsicht: Explosionsgefahr besteht trotzdem!) und stehen nun erstmals in voller Breite für weitere Untersuchungen zu Reaktivität und Eigenschaften zur Verfügung. Darüber hinaus zeigen wir, wie mit dieser Methode α-Azidoester, die als Bausteine für Aminosäuren fungieren können, gebildet werden.

An operationally simple, direct azidation of 1,3-dicarbonyl compounds has been developed. The reaction proceeds readily under ambient conditions using sodium azide and an iodine-based oxidant such as I₂ or 2-iodoxybenzoic acid (IBX)-SO₃K/NaI. In particular, the latter method, as a new and well-balanced oxidizing agent, shows excellent functional group tolerance and substrate scope and thus allows access to a variety of tertiary 2-azido and 2,2-bisazido 1,3-dicarbonyl compounds that would be more difficult to access by using traditional methods. Because the azide-containing products easily undergo 1,3-dipolar cycloaddition with alkynes, our report represents a novel route to analogues of sensitive complex molecules.