A route to the 9,10-secosteroid astrogorgiadiol featuring a key sp–sp Suzuki type cross-coupling

The described semi-synthetic route differs from the previously published approaches by an original C-7–C-8 disconnection. The kinetic enol triflate of Grundmann ketone was chosen as the CD-ring platform on which to couple an A-ring synthon via a challenging sp²–sp³ cross-coupling. A range of A-ring synthons was synthesized to allow the investigations of various conditions of metal-catalyzed couplings. Suzuki-type chemistry provided a useful (89% yield) answer. Whereas the last step of the designed route—a regioselective opening of the epoxide obtained from the alkene, product of the coupling reaction—proved more challenging than expected, a hydroboration endgame route completed a formal synthesis of (−)-astrogorgiadiol.     

Enhanced Photoinduced Electron Transfer at the Surface of Charged Lipid Bilayers

Photocatalytic systems often suffer from poor quantum yields due to fast charge recombination: The energy‐wasting annihilation of the photochemically created charge‐separated state. In this report, we show that the efficiency of photoinduced electron transfer from a sacrificial electron donor to positively charged methyl viologen, or to negatively charged 5,5′‐dithiobis(2‐nitrobenzoate), increases dramatically upon addition of charged phospholipid vesicles if the charge of the lipids is of the same sign as that of the electron acceptor. Centrifugation and UV/Vis titration experiments showed that the charged photosensitizers adsorb at the liposome surface, that is, where the photocatalytic reaction takes place. The increased photoelectron transfer efficiency in the presence of charged liposomes has been ascribed to preferential electrostatic interactions between the photosensitizer and the membrane, which prevents the formation of photosensitizer–electron‐acceptor complexes that are inactive towards photoreduction. Furthermore, it is shown that the addition of liposomes results in a decrease in photoproduct inhibition, which is caused by repulsion of the reduced electron acceptor by the photocatalytic site. Thus, liposomes can be used as a support to perform efficient photocatalysis; the charged photoproducts are pushed away from the liposomes and represent “soluble electrons” that can be physically separated from the place where they were generated.     

Terpy(Pt–salphen)2 Switchable Luminescent Molecular Tweezers

The design and synthesis of switchable molecular tweezers based on a luminescent terpy(Pt‐salphen)₂ ( 1 ; terpy=terpyridine) complex is reported. Upon metal coordination, the tweezers can switch from an open “W”‐shaped conformation to a closed “U”‐shaped form that is adapted for selective recognition of cations. Closing of the tweezers by metal coordination (M=Zn²⁺, Cu²⁺, Pb²⁺, Fe²⁺, Hg²⁺) was monitored by ¹H NMR and/or UV/Vis titrations. During the titration, exclusive formation of the 1:1 complex [M( 1 )] was observed, without appearance of an intermediate 1:2 complex [M( 1 )₂]. The crystallographic structure of the 1:1 complex was obtained with Pb²⁺ and showed a distorted helical structure. Selective intercalation of Hg²⁺ cations by the closed “U” form was observed. The tweezers were reopened by selective metal decoordination of the terpyridine ligand by using tris(2‐aminoethyl)amine (tren) as a competitive ligand without modification of the Pt–salphen complex. Detailed photophysical studies were performed on the open and closed tweezers. Structured emission was observed in the open form from the Pt–salphen moieties, with a high quantum yield and a long lifetime. The emission is slightly modified upon closing with 1 equivalent of Zn²⁺ or Hg²⁺, whereas a dramatic quenching was obtained upon intercalation of additional Hg²⁺.     

Diastereoselective Synthesis of Open‐Chain Secondary Alkyllithium Compounds and Trapping Reactions with Electrophiles

A practical stereoselective iodide–lithium exchange was used in the first general preparation of functionalized stereodefined acyclic secondary nonstabilized lithium reagents from the corresponding secondary alkyl iodides. These lithium reagents react with various electrophiles including carbon electrophiles with high retention of configuration. Kinetic data on the configurational stability of these acyclic alkyllithium reagents are given. This methodology offers a new entry to chiral synthons for the stereoselective synthesis of open‐chain molecules.     

From Syndiotactic Homopolymers to Chemically Tunable Alternating Copolymers: Highly Active Yttrium Complexes for Stereoselective Ring‐Opening Polymerization of β‐Malolactonates

Alternating copolymers constitute an attractive class of materials. It was shown previously that highly alternated poly(β‐hydroxyalkanoate)s (PHAs) can be prepared by ring‐opening polymerization (ROP) of mixtures of two different enantiomerically pure 4‐alkyl‐β‐propiolactones. However, the approach could not be extended to PHAs with chemically tunable functional groups, which is highly desirable to access original advanced materials. Reported herein is the first highly syndioselective and controlled ROP of racemic allyl and benzyl β‐malolactonates (MLA^R; R=allyl, benzyl) using an yttrium complex supported by a tetradentate dichloro‐substituted bis(phenolate) ligand. This highly active catalyst allows the nearly perfect alternating copolymerization of MLA^Allyl and MLA^Benzyl. Hydrogenolysis of the benzyloxycarbonyl or functionalization of the allyl pendant groups opens a route towards a new class of functional alternating copolymers.     

Spontaneous Biomimetic Formation of (±)‐Dictazole B under Irradiation with Artificial Sunlight

Guided by biosynthetic considerations, the total synthesis of dictazole B is reported for the first time. Experimental evidence for an easy access to challenging cyclobutane alkaloids of marine origin, which are often postulated to be biosynthetic precursors of more complex structures, is provided.     

Nitryl Cyanide,NCNO2

The elusive nitryl cyanide, NCNO₂, has been synthesized and characterized. It was prepared in good yield, isolated by fractional condensation, characterized by NMR and vibrational spectroscopy, and studied by theoretical calculations. Nitryl cyanide holds promise as a high energy density material (HEDM) and might also prove useful as a HEDM building block. The simplicity and inherent stability of nitryl cyanide, together with the known multitude of nitriles in interstellar space, suggest that the compound might also be a potential candidate for observations in atmospheric and interstellar chemistry.     

From Chitin to Bioactive Chitooligosaccharides and Conjugates: Access to Lipochitooligosaccharides and the TMG‐chitotriomycin

The direct and chemoselective N‐transacylation of peracetylated chitooligosaccharides (COSs), readily obtained from chitin, to give per‐N‐trifluoroacetyl derivatives offers an attractive route to size‐defined COSs and derived glycoconjugates. It involves the use of various acceptor building blocks and trifluoromethyl oxazoline dimer donors prepared with efficiency and highly reactive in 1,2‐trans glycosylation reactions. This method was applied to the preparation of the important symbiotic glycolipids which are highly active on plants and to the TMG‐chitotriomycin, a potent and specific inhibitor of insect, fungal, and bacterial N‐acetylglucosaminidases.     

Water-based conditions for the microscale parallel synthesis of bicyclic lactams

We report efficient miniaturized conditions to prepare arrays of bicyclic lactams for screening. The nature of the solvent is usually an important factor of reactivity. At a small synthesis scale, when automated pipetting devices are required, physical properties of the solvent, such as surface tension and vapor pressure also become very important. After having shown that a complete evaporation of a solution of reagents in water or a mixture of ethanol and water yields the expected lactams, we exemplified the reaction and procedure with the preparation of a library of 80 members. Our synthesis scheme is validated for synthesis scales from 1 to 100 mg. Therefore, it can be used both to produce rapidly test samples for HTS as well as to prepare intermediates for the synthesis of more elaborated nature-inspired compounds.