Bis Ring Closing Olefin Metathesis for the Synthesis of Unsaturated Polycyclic Ethers. O-Membered Ring Cyclization in Favor of C-Membered Ring Cyclization

O-Allylated Pudovik and Passerini Adducts as Versatile Scaffolds for Product Diversification

The palladium-catalyzed O-allylation of α-hydroxyphosphonates and α-hydroxyamides obtained from Pudovik and Passerini multicomponent reactions has allowed interesting and highly straightforward access to a variety of building blocks for product diversification. These post-functionalizations include a selective base- or ruthenium hydride-mediated isomerization/Claisen rearrangement cascade and a ring-closing metathesis that allows access to a variety of diversely functionalized phosphono-oxaheterocycles.

Rapid copolymerization of canola oil derived epoxide monomers with anhydrides and carbon dioxide (CO2)

A rapid synthesis of bio-based polyesters/polycarbonates from canola oil derived monomers and carbon dioxide/anhydrides using microwaves.

Multi-Bond Forming Processes in Efficient Synthesis

An increasing number of synthetic organic chemists are embracing the philosophy of efficiency. Herein we highlight multi-bond forming processes, which form two or more new covalent bonds in a single synthetic operation. Such processes, which have the ability to rapidly increase structural complexity, are preeminent in contemporary synthetic organic chemistry. In this short review we classify, analyse, and contrast contemporary multi-bond forming processes, frame these cutting edge contributions within a historical context, and speculate on likely future developments in the area.

Studies on synthesis and activation mechanism of mitomycin dimers connected by 1,2-dithiolane and diol linkers

We report the synthetic and mechanistic studies on a new cyclic disulfide mitomycin dimer, 7-N,7'-N'-(1″,2″-dithiolanyl-3″,5″-dimethylenyl)bismitomycin C (8), and a diol mitomycin dimer, 7-N,7'-N'-(2″,4″-dihydroxy-1″,5″-pentanediyl)bismitomycin C (9). Mitomycin 8 is a dimer connected by a 1,2-dithiolane (a five-membered cyclic disulfide) linker, and was specifically designed to undergo nucleophilic activation and double DNA alkylations leading to efficient production of DNA interstrand cross-link (DNA ISC) adducts. Disulfide cleavage in 8 would generate two thiol groups that could serve as probes to activate two mitomycin rings. At first, the target mitomycin 8 was synthesized using mitomycin A (1) and the key intermediate, cyclic disulfide (10), which was prepared through a seven-step synthetic sequence. Diol mitomycin 9 was also synthesized from 1 and diamine salt 13. Next, kinetic studies using solvolysis reaction revealed that the activation rates of 8 were much higher than those of 9 and mitomycin C (2) under nucleophilic conditions provided by Et(3)P presumably due to the presence of a cyclic disulfide unit in 8. These findings led us to propose a nucleophilic activation pathway for 8. Then, DNA ISC experiments further revealed that the levels of DNA ISC caused by 8 in the presence of Et(3)P were much higher (97%) than those by 9 (5%) and 2 (4%). More importantly, mitomycin 8 underwent much faster activation and produced slightly higher levels of DNA ISC than the previously reported mitomycins 5-7. Overall, we concluded that 8 was highly efficient for both nucleophilic activation and corresponding DNA ISC formation, and that this differentiation came from the crucial function of the cyclic disulfide unit in 8.

Synthesis of fused-ring and attached-ring bis-tetrahydrofurans via Pd-catalyzed carboetherification

A five step-synthesis of fused bis-tetrahydrofurans and attached bis-tetrahydrofurans from butadiene diepoxide is described. Two sequential Pd-catalyzed carboetherification reactions between protected 1,2-diols and aryl/alkenyl bromides, each of which form both a C-O bond and a C-C bond, are used to generate the heterocyclic rings with >20:1 dr. Installation of different R(1) and R(2) groups is achieved in a straightforward fashion through use of different aryl or alkenyl bromide coupling partners.

Synthesis of a Novel Ceramide Analogue and its Use in a High-Throughput Fluorogenic Assay for Ceramidases

Several investigations have shown that acid ceramidase inhibitors are potential antiproliferative and cytostatic drugs for cancer chemotherapy. The combinatorial chemistry approach for the discovery of acid ceramidase inhibitors requires the availability of a high-throughput enzyme assay. The synthesis of a novel fluorogenic ceramidase substrate, and its processing both in vitro and in cultured cells in a microtiter plate layout, are reported in this article. This coumarinic substrate was hydrolyzed in vitro (rat liver lysosomes) with Km and Vmax values of 113 microM and 3.6 pmol min-1 mg-1, respectively. Similarly, hydrolysis occurred in intact cultured cells that overexpressed acidic ceramidase. The assay was validated for the identification and characterization of acidic ceramidase inhibitors by using several alpha-ketoamide ceramide analogues, whose inhibitory activity had been previously described.

Stereoselective Syntheses of Enantiomerically Pure 2,5-disubstituted Dihydropyrans Based on Olefin Metathesis

A short synthesis of 2,5-disubstituted dihydropyrans starting from d-mannitol as a chiral building block is described. Our synthetic approach combines ruthenium-catalyzed ring closing olefin metathesis and palladium-catalyzed nucleophilic substitution.

Control of ring size selectivity by substrate directable RCM

Hydroxy groups may exert strong catalyst-directing effects in olefin metathesis reactions, which are exploited for a ring size-selective RCM reaction.

Free-Radical-5-exo-Trig Cyclization of Chiral 3-Silylhepta-1,6-dienes: Concise Approach to the A−B−C Ring Core of Hexacyclinic Acid

[Chemical reaction: See text] Free-radical-mediated 5-exo-trig cyclization of hepta-1,6-dienes 6a-c incorporating an allylsilane moiety was shown to provide at low temperature exclusively the trans-cis cyclopentanes 7a-c in good yield. In contrast, the same reaction with the alkyl analogue 9a led to the formation of all four possible stereoisomers. Interestingly, extension of this sequence of radical processes to alkoxy analogues 12-14 provided the complementary cis-cis stereoisomers with modest to excellent stereoselectivity. It is noteworthy that under such conditions allylsilanes were found to be much more reactive than their alkyl and alkoxy analogues. Beckwith-Houk-type models were proposed that rationalize the stereochemical course of these 5-exo-trig cyclizations. Finally, an illustration of the value of this methodology was proposed with the synthesis of the A-B-C tricyclic unit of polyketide hexacyclinic acid 3a.

7-N,7'-N'-(1",2"-Dithianyl-3",6"-dimethylenyl)bismitomycin C: synthesis and nucleophilic activation of a dimeric mitomycin

Dimeric alkylating agents that modify complementary DNA strands have engendered significant interest. We have prepared the novel dimeric mitomycin, 7-N,7'-N'-(1",2"-dithianyl-3",6"-dimethylenyl)bismitomycin C (9), in which the mitomycins are bridged by a dithiane unit. Dimer 9, like the clinically tested acyclic disulfides KW-2149 (3) and BMS-181174 (4), was designed to activate under nucleophilic and reductive conditions. Successive nucleophile-mediated disulfide cleavage transformations of 9 are expected to generate thiol species ideally positioned to render the two mitomycin systems vulnerable to nucleophilic attack and permit DNA interstrand cross-link formation. The dithiane linker, strategically positioned between the two mitomycins, distinguished 9 from 3 and 4. Nucleophilic activation of this cyclic disulfide permitted both activated mitomycins to remain tethered to one another. We report the synthesis of 9, and show that the nucleophile Et(3)P markedly enhances the activation and consumption of 9, compared with the reference compound 7-N, 7"-N'-(cyclohexanyl-trans-1",4"-dimethylenyl)bismitomycin C (27). We further demonstrated that provides higher levels of DNA interstrand cross-links than either the dimeric reference compounds, and 7-N,7-N'-(2",5"-dihydroxy-1",6"-hexanediyl)bismitomycin C (28), or the monomeric mitomycins, 1 and 3, when Et(3)P is added to solutions containing EcoRI-linearized pBR322 DNA.

New strategy for the construction of a monotetrahydrofuran ring in Annonaceous acetogenin based on a ruthenium ring-closing metathesis: application to the synthesis of Solamin

An original convergent total synthesis of Solamin (type A annonaceous acetogenin) was achieved. The central THF core was obtained by means of a ring-closing metathesis (RCM) reaction using a ruthenium imidazolylidene complex. The RCM substrate was prepared from a vinyl-substituted epoxide by reaction with an allyl alcohol, both synthesized from propargylic alcohol. The flexibility of the strategy should be useful in preparing various natural and unnatural annonaceous acetogenins.

C2-Symmetric enantiopure ethanotethered bis(alpha,beta-butenolides) as templates for asymmetric synthesis. Application to the synthesis of (+)-grandisol

Starting from D-mannitol, we have prepared several C(2)-symmetric ethanotethered bis(alpha,beta-butenolides) and studied their [2+2] photocycloaddition reaction with ethylene. The protective groups of the central diol unit have a noticeable influence on the facial selectivity of the cycloaddition, the bis(trimethylsilyloxy) derivatives showing the highest diastereoselectivity. A theoretical conformational analysis of the substrates in the ground state is in good agreement with the diastereofacial selectivity experimentally observed. The bis(photocycloadducts) have been converted into the enantiopure cyclobutanes formally derived from the photoreaction of ethylene with gamma-hydroxymethyl-alpha,beta-butenolide, in which only a moderate facial selectivity had been previously found. As an application of these studies, we have developed a highly efficient and stereoselective synthesis of (+)-grandisol.

Efficiency of a ruthenium catalyst in metathesis reactions of sulfur-containing compounds

[reaction: see text] 1,3-Dimesitylimidazol-2-ylidene ruthenium benzylidene catalyst (RuCl2(=C(H)Ph)(PCy3)(IMes)) has been successfully employed in ring-closing metathesis reactions of acyclic diene sulfides, disulfides, and dithianes and in self-cross metathesis reactions of ene-sulfides, thioethers, and thiols.