Regioselective Double Capping of Cyclodextrin Scaffolds

Abstract

Four different regioselective double capping reactions were applied either to α- or β-cyclodextrin (CD) scaffolds. The first, which relied on the use of a rigid, bulky dialkylating reagent containing two trityl-like subunits, gave access to an A,B,D,E-tetrafunctionalised β-CD regioisomer in large scale reactions. Two further capping reactions, involving the dianions PhP(2-) and S(2- , led to the synthesis of new C(1)-symmetrical β-cyclodextrins in which pairs of neighbouring glucose units are linked by very short spacers. The last double capping reaction described allowed the high-yield preparation of unprecedented α- and β-cyclodextrins containing two sulfate handles. Proximal capping turned out to be favoured for each of the above difunctional reagents. The structural characterisation of the capped species was achieved by thorough NMR investigations as well as by single-crystal X-ray diffraction studies.

Confining Phosphanes Derived from Cyclodextrins for Efficient Regio‐ and Enantioselective Hydroformylation

“…[10] However, it is generally believed that high isoselectivity is incompatible with high enantioselectivity and vice versa. [11] We now describe the high performance of two crowded, chiral phosphanes, namely HUGPHOS-1 [12] and HUGPHOS-2, [13] in the asymmetric hydroformylation of styrene. Both ligands, which are respectively derived from a-and bcyclodextrin, have their phosphorus lone pair directed towards the appended cyclodextrin (CD) core.…”

Phosphinocyclodextrins as confining units for catalytic metal centres. Applications to carbon–carbon bond forming reactions

“…We observed that by raising the temperature to 130 °C, the conversions remained practically unchanged (Table 3, entry 6). For comparison purposes, we also assessed the catalytic behaviour of the related diphosphine WIDEPHOS [39,52]. When using a WIDEPHOS:Pd ratio of 1:1, practically no reaction occurred (Table 3, entry 5).…”

“…In order to determine the enantiomeric excess, a sample of the reaction mixture (toluene) was treated with LiAlH 4 for 0.5 h. After filtration, the toluene solution containing enantiomeric alcohols was analysed by GC with a Chirasil-DEX CB column (25 m × 0.25 mm). HUGPHOS-1, HUGPHOS-2 [38], WIDEPHOS [39], and [PdCl(dmba)] 2 [89], were synthesized according to literature procedures. The synthesis and characterisation of compounds 5 , 9 , 12 and 13, as well as the general procedure for rhodium catalysed hydroformylation reactions have been reported in a preliminary communication [44].…”

“…However, when it comes to enantioselectivity, only one chiral mono-P(III) ligand [30–32] has so far shown some potential in the notoriously challenging, but industrially relevant asymmetric hydroformylation [33–37]. Recently, we have synthesised a new type of chiral phosphine ligand (HUGPHOS-1 [38] and HUGPHOS-2 [39], see Fig. 1), which consists of methylated cyclodextrins (CD) equipped with an embedded phosphorus atom.…”

Confining Phosphanes Derived from Cyclodextrins for Efficient Regio‐ and Enantioselective Hydroformylation

“…We now describe the high performance of two crowded, chiral phosphanes, namely HUGPHOS‐112 and HUGPHOS‐2,13 in the asymmetric hydroformylation of styrene. Both ligands, which are respectively derived from α‐ and β‐cyclodextrin, have their phosphorus lone pair directed towards the appended cyclodextrin (CD) core.…”