Reactions of Alkenyl Fischer Carbene Complexes with Ketene Acetals: Formation of Alkynes

Wang, Siu Ling B.; Liu, Xuejun; Ruiz, Miriam C.; Gopalsamuthiram, Vijay; Wulff, William D.

doi:10.1002/ejoc.200600672

Cited by 11 publications

(5 citation statements)

References 60 publications

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“…The attempted cyclopropanation reaction of alkenylcarbene complexes 16 with ketene acetal 283 resulted in the unexpected isolation of dihydrocoumarin 284 (Scheme ) . This finding has been rationalized in terms of an isolable alkyne intermediate I generated by the reaction of the ketene acetal with the carbene complex.…”

Section: Multistep and Multicomponent Reactionsmentioning

confidence: 99%

Fischer Carbene Complexes in Organic Synthesis: Metal-Assisted and Metal-Templated Reactions

2009

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Section: Multistep and Multicomponent Reactionsmentioning

confidence: 99%

Fischer Carbene Complexes in Organic Synthesis: Metal-Assisted and Metal-Templated Reactions

2009

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“…All four stereoisomers of 5 were isolated in a single fraction. 9 was previously described as a side product in a synthetic scheme (30). …”

Section: Figuresmentioning

confidence: 99%

Exploiting a Global Regulator for Small Molecule Discovery in Photorhabdus luminescens

2010

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Bacterially-produced small molecules demonstrate a remarkable range of structural and functional diversity and include some of our most useful biological probes and therapeutic agents. Annotations of bacterial genomes reveal a large gap between the number of known small molecules and the number of biosynthetic genes/loci that could produce such small molecules, a gap that most likely originates from tight regulatory control by the producing organism. This study coupled a global transcriptional regulator, HexA, to secondary metabolite production in Photorhabdus luminescens, a member of the Gammaproteobacteria that participates in a complex symbiosis with nematode worms and insect larvae. HexA is a LysR-type transcriptional repressor, and knocking it out to create a P. luminescens ΔhexA mutant led to dramatic upregulation of biosynthesized small molecules. Use of this mutant expanded a family of stilbene-derived small molecules, which were known to play important roles in the symbiosis, from three members to at least nine members.Photorhabdus luminescens, a Gammaproteobacterium, uses a functionally diverse suite of secondary metabolites to participate in a complex symbiosis with nematode worms (Heterorhabditis spp.) and insect larvae. The bacteria persist quietly in the guts of infective juvenile (IJ) nematodes that hunt insect larvae. When a worm succeeds in entering its prey's circulatory system (hemolymph), it regurgitates the bacteria, which then proceed to make toxins that kill the larva, proteases and esterases that liquefy the larva's interior, signals that cause the IJ worms to become reproducing adults, molecules that counter insect defense mechanisms, and molecules that protect their prey from competing bacteria and fungi. Some of the small molecules produced by P. luminescens have been identified (1), but despite efforts in many laboratories, these known small molecules represent only a small fraction of the bacteria's metabolic potential. The sequenced P. luminescens genome contains at least 33 genes in 20 loci that encode proteins similar to polyketide synthases, nonribosomal peptide synthetases, and β-lactam-producing enzymes (2). The genomic potential for secondary metabolism seen in P. luminescens rivals members of the Streptomyces genus, the most productive antibiotic-producing bacterial genus (3).To access these uncharacterized small molecules, we searched for the molecular signals and their targets that control P. luminescens metabolism. Recently we reported that the bacteria respond to the high concentrations of L-proline in insect hemolymph by initiating a profound upregulation of secondary metabolite production (4). L-proline enhances the production of small molecules known to be involved in antibiosis, insect virulence, and nematode mutualism along with many structurally and functionally uncharacterized † Corresponding author, jon_clardy@hms.harvard.edu. * These authors contributed equally to this work. molecules. L-proline acts both as an osmoprotectant in the high solute concentrat...

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“…The preparation and characterization of most of the carbene complexes employed in this study have been previously described, including the aryl complexes 1a and 1b , the isopropenyl complex 20a , the trans -propenyl complexes 23a and 23b , the sec -butenyl complex 25a , the cyclohexenyl complex 28 , and the methyl complex 47 …”

Section: Methodsmentioning

confidence: 99%

Alkyne Competition in the Benzannulation Reaction with Chromium Carbene Complexes

Berbasov

Wulff

2010

J. Org. Chem.

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The benzannulation reaction of Fischer carbene complexes is investigated under conditions where the reaction of the carbene complex is occurring in the presence of two different alkynes. A series of competition experiments are examined where the effects of various structural factors are explored by pitting 10 different carbene complexes with 11 different alkynes. Terminal alkynes will react selectively over internal alkynes in all cases examined including both aryl and alkenyl complexes. Aryl carbene complexes with methoxy substituents do not give quite as high selectivity for terminal alkynes over internal alkynes (∼95:5) as do isopropoxy substituents (>99:1), whereas most alkenyl complexes give high selectivity with both substituents (>99:1). Competition experiments between two different terminal alkynes or between two different internal alkynes did not result in anything more than very modest selectivities at best (∼2:1). Excellent selectivities were realized between two different terminal acetylenes if one of the terminal acetylene was protected with a trimethylsilyl group. Finally, it was demonstrated that the high selectivities between terminal and internal alkynes can be utilized in the reaction with molecules that contain both types of alkyne functions.

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Reactions of Alkenyl Fischer Carbene Complexes with Ketene Acetals: Formation of Alkynes

Cited by 11 publications

References 60 publications

Fischer Carbene Complexes in Organic Synthesis: Metal-Assisted and Metal-Templated Reactions

Fischer Carbene Complexes in Organic Synthesis: Metal-Assisted and Metal-Templated Reactions

Exploiting a Global Regulator for Small Molecule Discovery in Photorhabdus luminescens

Alkyne Competition in the Benzannulation Reaction with Chromium Carbene Complexes

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