A Straightforward Approach to Tetrahydroindolo[3,2‐b]carbazoles and 1‐Indolyltetrahydrocarbazoles through [3+3] Cyclodimerization of Indole‐Derived Cyclopropanes

A rapid new approach to produce biologically relevant bisindoles, namely indolyltetrahydrocarbazoles and indolo[3,2‐b]carbazoles, has been developed, based on the Ga(OTf)₃‐catalyzed [3+3] cyclodimerization of indole‐derived donor–acceptor cyclopropanes. Chemoselectivity of the process depends on the location of the three‐membered ring at the indole core.     

Design and synthesis of conformationally constrained, extended and reverse turn pseudopeptides as Grb2-SH2 domain antagonists

A series of conformationally constrained and flexible pseudopeptide derivatives of the tripeptide pYVN were prepared as potential antagonists of interactions of phosphotyrosine peptides with the Grb2-SH2 domain. The conformationally constrained compounds contained trans- and cis-cyclopropanes as replacements to enforce locally extended and reverse turn peptide conformations, respectively.     

Copper-catalyzed electrosynthesis of 1-acyl-2,2-diphenylcyclopropanes and their behaviour in acidic medium

The formation of 1-acyl-2,2-diphenylcyclopropanes is performed under mild electrochemical conditions. These cyclopropane derivatives, through acid-catalyzed ring-opening, lead to γ,γ-diphenyl-β,γ-unsaturated carbonyl compounds which evolve into either substituted naphthalenes, or β-benzhydryl-α,β-cycloalkenones depending on the acyclic or cyclic nature of the intermediate allyl ketone.     

gem‐Dihalocyclopropanes as Building Blocks in Natural‐Product Synthesis: Enantioselective Total Syntheses of ent‐Erythramine and 3‐epi‐Erythramine

ent‐Erythramine ((?)‐ 1 ), the enantiomer of the alkaloid erythramine, was prepared in 15 steps from known compounds. The first of three pivotal bond‐forming steps in the synthesis was a Suzuki–Miyaura cross‐coupling reaction of the starting materials to give a bis‐silyl ether. The second involved silver(I)‐induced electrocyclic ring opening of the gem‐dichlorocyclopropane formed in the next step and trapping of the ensuing π‐allyl cation by the tethered nitrogen atom to give, following cleavage of the allyloxycarbonyl protecting group, an approximately 5:6 mixture of the chromatographically separable diastereoisomeric spirocyclic products. In the third critical bond‐forming reaction, the iodide formed from one of the diastereoisomers underwent a radical‐addition/elimination reaction sequence that led to (?)‐ 1 in 89 % yield. The application of the same sequence of transformations to the other diastereoisomer afforded 3‐epi‐(+)‐erythramine (3‐epi‐(+)‐ 1 ).     

Reaction of diazoalkanes with unsaturated compounds. 11. Relative reactivity of olefins on catalytic cyclopropanation with diazomethane and palladium catalysts

The relative reactivity of unsaturated compounds on catalytic cyclopropanation with diazomethane in the presence of catalysts based on Pd²⁺ [Pd(OAc)₂, Pd(acac)₂, (PPh₃)₂·PdCl₂] has been studied using competing reactions. An interconnection was shown between the relative reactivity of the olefins and the coordinating activity of the C=C bond depending on its strain and spatial environment.For previous communication, see [1].Institute of Organic Chemistry, Urals Branch, Russian Academy of Sciences, 450054 Ufa; N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2353–2361, October, 1992.     

Rhodium‐Catalyzed Enantioselective Silylation of Cyclopropyl C−H Bonds

Hydrosilyl ethers, generated in situ by the dehydrogenative silylation of cyclopropylmethanols with diethylsilane, undergo asymmetric, intramolecular silylation of cyclopropyl C?H bonds in high yields and with high enantiomeric excesses in the presence of a rhodium catalyst derived from a rhodium precursor and the bisphosphine (S)‐DTBM‐SEGPHOS. The resulting enantioenriched oxasilolanes are suitable substrates for the Tamao–Fleming oxidation to form cyclopropanols with conservation of the ee value from the C?H silylation. Preliminary mechanistic data suggest that C?H cleavage is likely to be the turnover‐limiting and enantioselectivity‐determining step.     

Cobalt‐Catalyzed Tandem C−H Activation/C−C Cleavage/C−H Cyclization of Aromatic Amides with Alkylidenecyclopropanes

A cobalt‐catalyzed chelation‐assisted tandem C?H activation/C?C cleavage/C?H cyclization of aromatic amides with alkylidenecyclopropanes is reported. This process allows the sequential formation of two C?C bonds, which is in sharp contrast to previous reports on using rhodium catalysts for the formation of C?N bonds. Here the inexpensive catalyst system exhibits good functional‐group compatibility and relatively broad substrate scope. The desired products can be easily transformed into polycyclic lactones with m‐CPBA. Mechanistic studies revealed that the tandem reaction proceeds through a C?H cobaltation, β‐carbon elimination, and intramolecular C?H cobaltation sequence.     

Toblerols: Cyclopropanol‐Containing Polyketide Modulators of Antibiosis in Methylobacteria

Trans‐AT polyketide synthases (PKSs) are a family of biosynthetically versatile modular type I PKSs that generate bioactive polyketides of impressive structural diversity. In this study, we detected, in the genome of several bacteria a cryptic, architecturally unusual trans‐AT PKS gene cluster which eluded automated PKS prediction. Genomic mining of one of these strains, the model methylotroph Methylobacterium extorquens AM1, revealed unique epoxide‐ and cyclopropanol‐containing polyketides named toblerols. Relative and absolute stereochemistry were determined by NMR experiments, chemical derivatization, and the comparison of CD data between the derivatized natural product and a synthesized model compound. Biosynthetic data suggest that the cyclopropanol moiety is generated by carbon–carbon shortening of a more extended precursor. Surprisingly, a knock‐out strain impaired in polyketide production showed strong inhibitory activity against other methylobacteria in contrast to the wild‐type producer. The activity was inhibited by complementation with toblerols, thus suggesting that these compounds modulate an as‐yet unknown methylobacterial antibiotic.     

Acylation of phenols with γ-chlorobutyroyl chloride and transformations of the reaction products

Alkylphenols afford only O-acyl derivatives on treatment with -chlorobutyroyl chloride in the presence of both Et₃N and AIC1₃ at 20–60 °C. They cyclize under the action of K₂CO₃ in DMSO into the respective cyclopropanes and undergo Fries rearrangement on heating with AICl₃ at 120 °C into C-acyl derivatives.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 1023–1025, April, 1996.