Synthesis and photonics of polyfunctional conjugated polyenes

Methods for the synthesis of various types of polyfunctional conjugated polyenes based on aminals of unsaturated -amino aldehydes are surveyed. The influence of the interaction of chromophores on the photophysical properties of polyene bis(amino)-substituted ketones and polymethine salts based on them as well as on the properties of absorption and fluorescence spectra of the cation-anionic polymethine dyes are considered.     

Synthesis of sterically hindered enamides via a Ti-mediated condensation of amides with aldehydes and ketones

The first TiCl(4)-mediated condensation of secondary amides with aldehydes and ketones has been achieved. The reaction proceeds at room temperature and is complete within 5 h in most cases. The optimized procedure used 5 equiv of an amine base hinting that the in situ activation of both the amide and the Lewis acid is required. The reaction affords polysubstituted (E)-enamides.     

Polyene condensation of aldehydes

Summary The effects of catalyst, temperature, and duration of reaction were studied for the polyenic condensation of crotonaldehyde and senecialdehyde.     

Cycloadditions of 2-azaallyllithium species with conjugated polyenes

2-Azaallyllithium species [R(1)CH(-)N=C(X)R(2)Li(+), where R(1) and R(2) are alkyl and X = OMe] were generated by tin-lithium exchange of (2-azaallyl)stannanes and underwent [pi4s+pi2s] and [pi6s+pi4s] cycloadditions with cyclic dienes and trienes, respectively, to generate novel bridged azabicyclic compounds in a highly diastereoselective endo fashion. The periselectivity using cycloheptatriene was modest, producing a 1:1 mixture of [pi6s+pi4s] and [pi4s+pi2s] adducts. The reactions of 2-azaallyllithium species with dienes proceeded by a [pi4s+pi2s] pathway. The cycloadducts derived from cyclic 2-azaallyllithium species possess the 7-azabicyclo[2.2.1]heptane (tropane) or 8-azabicyclo[3.2.1]octane ring system and have been elaborated into cocaine-like analogues.     

Synthesis of pyrazolines by the condensation of monoalkyl hydrazones with aldehydes

Acetaldehyde readily condenses with its monalkyl hydrazones with the formation of 1-alkyl-5-methyl-2-pyrazolines. A number of pure 2pyrazolines have been synthesized in this way with yields of 40–60%. In the condensation of propionaldehyde with its isopropyl hydrazone, because of the occurrence of rearrangements and the nonstereospecificity of the process, a mixture of structural and stereoisomeric 2-pyrazolines is formed. The promising condensation of aldehydes with monalkyl hydrazones of other aldehydes and ketones is accompanied by transhydrazonation, which limits the preparative possibilities of this reaction.From the text of the thesis of N. B. Burmanova, defended in May, 1967.     

Synthesis of (-)-quinocarcin by directed condensation of alpha-amino aldehydes

An enantioselective synthesis of the natural antiproliferative agent quinocarcin was achieved by the directed condensation of optically active alpha-amino aldehyde intermediates. Condensation of the N-protected alpha-amino aldehyde 1, prepared in eight steps (19% yield) from (R,R)-pseudoephedrine glycinamide, with the C-protected alpha-amino aldehyde derivative 2, prepared in seven steps (34% yield) from (R,R)-pseudoephedrine glycinamide, afforded the corresponding imine in quantitative yield. Without isolation, direct treatment of this imine intermediate with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and hydrogen cyanide led to cleavage of the fluorenylmethoxycarbonyl (Fmoc) protective group followed by addition of cyanide (Strecker reaction) to form the bis-amino nitriles 3 as a mixture of diastereomers, in 91% yield. Treatment of the diastereomers 3 with trimethylsilyl cyanide and zinc chloride in 2,2,2-trifluoroethanol at 60 degrees C led to stepwise cyclization to form the tetracyclic product 4 (42% yield from 1 and 2). The latter intermediate was transformed into (-)-quinocarcin (1) in five steps (45% yield). The yield of quinocarcin was 19% from 1 and 2 (7 steps), and 4% from pseudoephedrine glycinamide (15 steps).     

Isomer combinatorics for acyclic conjugated polyenes: enumeration and beyond

A combinatorial approach to fully conjugated acyclic polyenes (C _N H _{N +2}) is considered with a view to the extension of standard enumeration techniques to treat a widened range of chemically interesting features. As a first step, enumerations are made respecting: placement of single and double bonds, the occurrence of cis/trans isomers, and the degree (and type) of “radicality” of such conjugated networks. As a further extension, several structural (graph-theoretic) invariants averaged over various types of isomer classes and sub-classes are made, and then these invariants are utilized to estimate several physicochemical properties averaged over these same classes or sub-classes. The properties currently so considered are heats of formation, indices of refraction, and magnetic susceptibilities. Finally, the asymptotic behaviors of isomer counts and isomer properties in the many-atom limit is elaborated. Received: 10 August 1998 / Accepted: 17 November 1998 / Published online: 16 March 1999     

Synthesis of substituted stilbenes via the Knoevenagel condensation

Knoevenagel condensations between aldehydes and substrates containing active methylene groups were carried out in ethanol at room temperature, in the presence of potassium phosphate, to afford unsymmetrical olefins. These condensations have been shown to afford only the E-isomers in greater than 80% yields. Salicylaldehyde first produces the Knoevenagel condensation products, which undergo a subsequent heterocyclization to give coumarin derivatives. The structures of the synthesized compounds were established on the basis of UV, IR, MS and NMR spectroscopy.     

Synthesis of tetra- and octahydroxanthene derivatives by the condensation of dimedone with aromatic aldehydes

The reaction of dimedone with salicyl and 2-hydroxy-1-naphthoyl aldehydes gave derivatives of tetrahydroxanthene and tetrahydrobenzo[a]xanthene and not aldimedone as occurs in condensations with other aldehydes. Derivatives of decahydroacridine were obtained by reaction of the tetrahydroxanthene derivatives with methyl-and ethylamine. Tetrahydro- and octahydroxanthene derivatives were obtained from the reaction of acetylsalicylaldehyde with dimedone in acetic anhydride. The structures of the ketoenol forms of the products containing a-ketoenol unit were determined by¹H and¹³C NMR spectroscopy, and the mechanism of their interconversion is discussed.Institute of Bioorganic Chemistry, Belarus Academy of Science, Minsk, 220141. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 742–753, June, 1996. Original article submitted February 22, 1996.     

Solvent-free condensation of arylacetonitrile with aldehydes

The condensation of a series of arylacetonitriles with aldehydes can be carried out by mixing equivalent amounts of reagents with neat powdered KOH at room temperature for 3-60 min depending on the aldehyde steric hindrance. At higher temperature (110 °C), yields were generally higher and purity increased within very short reaction times (1-5 min). With pentamethylphenylacetonitrile, a phase transfer agent was necessary to give a satisfactory yield.     

Synthesis of conjugated nitroalkenes via nitroselenenylation of alkenes

Addition of silver nitrite to 2-bromoalkyl phenyl selenide in the presence of mercury(II) chloride afforded 2-nitroalkyl phenyl selenide, which upon oxidative deselenenylation provided the conjugated nitroalkene in excellent yield.     

Facile route to benzils from aldehydes via NHC-catalyzed benzoin condensation under metal-free conditions

A simple and efficient one-pot procedure for the synthesis of α-diketones from aldehydes via benzoin condensation under the influence of a catalytic amount of azolium salt combined with DBU has been developed. Thus, aldehyde was allowed to react with the azolium salt/DBU catalytic system at room temperature, and then the reaction mixture was heated to 70 °C under air atmosphere to afford the corresponding 1,2-diketone in good yield. This would be an efficient alternative method of synthesizing α-diketones from aldehydes under metal-free conditions.     

Synthesis of conjugated γ- and δ-lactones from aldehydes and ketones via a vinylation(allylation)-ring closing metathesis-oxidation sequence

Nucleophilic C-vinylation and C-allylation of aldehydes and ketones followed by O-allylation of the obtained carbinols gave the corresponding allyl or homoallyl ethers, respectively. Ring-closing metathesis of these compounds afforded in many cases cyclic ethers (dihydrofurans and dihydropyrans, respectively) bearing disubstituted and trisubstituted CC bonds. These were then subjected to allylic oxidation to yield conjugated γ- and δ-lactones. Reasons for the observed failures are presented and discussed.     

Synthesis of dialkoxydiphenylsilanes via the rhodium-catalyzed hydrosilylation of aldehydes

The commercially available rhodium(I) complex [RhCl(CO)₂]₂ (1) was shown to be an effective catalyst for the reduction of carbonyls with organosilanes under mild conditions. This study focusses on the hydrosilylation of aldehydes with diphenylsilane leading to the isolation of a series of dialkoxydiphenylsilanes with low catalytic loading of complex 1.     

MCSCF study of polaron- and bipolaron-like defects in smallall-trans conjugated polyenes

Summary A Multiconfigurational Self-Consistent Field study of neutral, singly and doubly ionized C₄H₆, C₆H₈, C₈H₁₀, and C₁₀H₁₂ as model systems for polaron and bipolaron defects in polyacetylene has been carried out. In all computations a double zeta quality basis set was used. The post-Hartree-Fock computations were carried out in the complete active subspace and the fully optimized structures are reported. Comparison with SCF results reveals that the inclusion of electron correlation attenuates the double bond/single bond alternancy in conjugated polyenes as well as the charge waves associated with the cations.Dedicated to Prof. Klaus Ruedenberg     

One-pot synthesis of trisubstituted conjugated dienes via sequential Suzuki-Miyaura cross-coupling with alkenyl- and alkyltrifluoroborates

The sequential, stereoselective disubstitution of 1,1-dibromoalkenes using a variety of alkenyltrifluoroborates followed by alkyltrifluoroborates in the presence of Pd(PPh3)4 is described. This synthetic method proceeds smoothly in one pot under mild reaction conditions to provide the corresponding trisubstituted, conjugated dienes in excellent yield. Moreover, the method is operationally very simple because the organotrifluoroborates are stable in air, and the byproducts are innocuous inorganic salts.     

Synthesis of 5,15-diarylporphyrins via orthoesters condensation with aryldipyrromethanes

General access to 5,15-diarylporphyrins in two steps is described. Generalization of this approach to tetra-substituted porphyrins allows the reproducible preparation of compounds, in some cases with high yields for porphyrins, which can be used in photodynamic therapy (PDT) in cancer today.