Magnaldehydes B and E along with their 4′-methylated derivatives are naturally occurring 2,4′-biphenols that have been isolated from the Magnoliaceae. Herein, these natural products have been synthesized from a common intermediate, which was obtained by a microwave-promoted, heterogeneously catalyzed, and protecting-group-free Suzuki–Miyaura coupling reaction in an aqueous medium. These reaction conditions were also successfully applied to a one-step synthesis of the slime mold metabolite dictyobiphenyl B.

Allyl, dimethylallyl and prenyl ethers derived from o-acylphenols reacted upon microwave irradiation to form C-allylated or -prenylated chromone derivatives, depending on the substitution pattern of the arene and the allyl substituent. The reaction proceeds through a tandem Claisen rearrangement and 6-endo-trig or 6-endo-dig cyclization sequence. For prenyl ethers, the tandem sequence can be extended by a Cope rearrangement to furnish 6-prenylchromones. The method is potentially useful for the synthesis of natural products and drugs.

Unlike their ortho counterparts, meta- and para-acetamidoanilines can be converted into the corresponding acetamidoarenediazonium salts. These offer various opportunities for multiple Pd-catalyzed arene functionalization reactions, such as Matsuda–Heck-, Suzuki–Miyaura- or Fujiwara–Moritani couplings.

The rare carbohydrate L-(+)-noviose was synthesized from enantiomerically pure L-lactate. The configuration at C-4 was established by diastereoselective nucleophilic addition to an in-situ-generated lactaldehyde. The resulting homoallylic alcohol was further transformed into a set of ring-closing metathesis (RCM) precursors. These compounds were converted into noviose in few steps using RCM and RCM–allylic-oxidation sequences.

Acetanilides can be deacetylated and diazotized in situ, and subsequently used in Pd-catalyzed coupling reactions without isolation of the diazonium intermediate. Heck reactions, Suzuki cross-coupling reactions, and a Pd-catalyzed [2+2+1] cycloaddition have been investigated as terminating CC bond-forming steps of this one-flask sequence. The sequence does not require the exchange of solvents or removal of by-products between the individual steps, but proceeds by addition of reagents and catalysts in due course.

A one-flask reaction sequence comprising ring closing metathesis (RCM) of butenoates derived from allylic alcohols and a base-mediated ring opening gives 2Z,4E-configured dienoic acids in high yields and stereoselectivities. Application of the method to the synthesis of the natural product fusanolide A suggests that the originally published structure was erroneously assigned and should be revised.

2,5-Disubstituted furans were synthesized by one-flask Heck arylation/oxidation sequences. The starting materials are 2-substituted 2,3-dihydrofurans, conveniently available by RCM/isomerization sequences, and arenediazonium salts. These react in ligand-free Heck reactions to afford 2,5-disubstituted 2,5-dihydrofurans, which are oxidized to the corresponding furans without isolation or intermediate workup. The oxidation is conveniently achieved with chloranil or DDQ, depending on the substrate.

Butenolides, obtained by ring-closing metathesis (RCM) of acrylates, undergo quantitative deprotonation with amide bases. Trapping of the resulting anions with electrophiles, for example, chlorophosphates, give furans. Subsequent Diels–Alder reaction and acid-catalysed rearrangement of the resulting oxabicyclonorbornadienes give substituted benzenes.

A protected derivative of (3R,4R)-hexa-1,5-diene-3,4-diol, a conveniently accessible C₂-symmetric building block, undergoes single or double cross metathesis with methyl acrylate. The cross metathesis products are amenable to stereoselective conjugate addition reactions and can be converted into either γ-butyrolactones or γ-lactams.

Alkynes and phenol diazonium salts undergo a Pd-catalyzed [2+2+1] cyclization reaction to spiro[4,5]decatetraene-7-ones. This structure was confirmed for one example by X-ray single-crystal structure analysis. The reaction is believed to proceed through oxidative addition of the phenol diazonium cation to Pd⁰, subsequent insertion of two alkynes, followed by irreversible spirocyclization.

Significantly better yields were achieved in Mizoroki–Heck reactions using 4-phenoldiazonium salts instead of their O-alkylated analogues under otherwise identical conditions. We found that a one-flask deacetylation–diazotation–precipitation sequence starting from paracetamol or acetanilides derived thereof provides a convenient access to the required diazonium tetrafluoroborates. The utility of these arylating agents in palladium-catalyzed CC bond forming reactions was demonstrated for a one-flask-synthesis of the heterocyclic core of the drug aripiprazole. Notably, the diazonium salt formation from an acetanilide could be combined with two Pd-catalyzed steps in a one-flask sequence, without any exchange of solvents or isolation of intermediates.

The efficiency of ring-closing metathesis (RCM) reactions of various acrylates to form 2 (5 H)-furanones, catalyzed by second-generation ruthenium complexes, is investigated in detail. In particular the effects of substrate concentration and substrate structure were studied for indenylidene and benzylidene catalysts, both of which are shown to catalyze the RCM reaction in good yields. The starting substrate concentration is shown to be an important factor in the reaction, as, at excessive initial substrate concentrations, irreversible catalyst deactivation seems to occur, whereas high catalyst loadings appear to be unnecessary.

All stereoisomers of the natural product centrolobine are selectively synthesized, by starting from a common precursor. Key steps are an enantioselective allylation with enantiomerically pure allylsilanes, a tandem ring-closing metathesis–isomerization reaction, and a Heck reaction by using an arene diazonium salt. By choosing appropriate conditions for the final deprotection step, either the cis-configured centrolobines or their epimers are selectively obtained.

Deoxy glycals can be synthesized from a mannitol-derived C₂-symmetric diene diol by using the tandem RCM/isomerization approach. Incorporation of a ruthenium-catalyzed dehydrogenative silylation step into the reaction sequence is possible. Thus, an orthogonally protected 3-deoxy glycalresults via a tandem RCM/hydrosilylation/isomerization sequence. All ruthenium-catalyzed steps of this tandem sequence occur under distinct conditions, allowing for the selective synthesis of the intermediates. The 3-deoxy glycals obtained via this route undergo a regio- and stereoselective Heck reaction, as exemplified by the synthesis of a C-aryl glycoside. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Protected 3,6-dideoxyglycals have been synthesized de novo as single isomers starting from ethyl lactate by using the tandem RCM–isomerization reaction as the key step. Different relative configurations become accessible by addition of vinyl- or allyl–metal compounds to protected lactaldehydes under Cram-chelate or Felkin–Anh control. The concept is exemplified for glycals of L-rhodinose and L-amicetose, as well as for ring-expanded non-natural analogues thereof. This novel approach to glycals is also applicable to the synthesis of disaccharide glycals via a reiterative strategy, as exemplified for the dimer of L-rhodinose and its non-natural ring expanded analogue.