Hydration with mercuric acetate and the reduction with 9-BBN-H of 2-(1-alkenyl)-4,6-dimethyl-s-triazines

Oxymercuration-demercuration of a double bond in conjugation with the 4,6-dimethyl-s-triazin-2-yl substituent as in alkenes 1a,b gave anti-Markovnikov regioselectivity, which is explained by the electron-withdrawing nature of the triazinyl substituent. However, hydroboration of the conjugated alkenes with 9-BBN-H gave the corresponding alkanes 5a-c under normal workup conditions with or without oxidation. With time and without workup the hydroboration of 1b gave spectral evidence for the formation of intermediates 9-13 resulting from the migration of the 9-BBN moiety from the alpha-carbon to a ring nitrogen with concurrent formation of an exocyclic double bond to an alpha-carbon of the ring. Hydrolysis of the intermediates gave 5a-c. A possible mechanism involving successive allylic rearrangements is presented.     

Synthesis of the all-cis-trimethyldecalin fragment of unusual terpenes by radical-mediated protonolysis of an alkylboron derivative

The synthesis of an enantiopure building-block with a contiguous all-cis-trimethyldecalin motif embedded in unusual terpenes is described. Starting from the Wieland–Miescher ketone, the key step is a one-pot hydroboration of an exocyclic methylene double bond promoted by disiamylborane and radical-mediated protonolysis of the corresponding alkylborane using 4-tert-butylcatechol.     

Catalytic asymmetric synthesis of chromenes and tetrahydroquinolines via sequential allylic alkylation and intramolecular Heck coupling

Highly enantioselective synthesis of chiral chromenes and tetrahydroquinolines is achieved by combining asymmetric copper-catalyzed allylic substitution with Grignard reagents and an efficient intramolecular Heck reaction. Moreover, the exocyclic double bond formed in the cyclisation was subjected to RCM, hydroboration and hydrogenation illuminating the synthetic versatility of these heterocycles.     

Oxidation of primary alcohols to aldehydes with oxygen catalysed by tetra-n-propylammonium perruthenate

The liquid-phase oxidation of a series of saturated and unsaturated non-allylic alcohols to aldehydes with oxygen or air catalysed by tetra-n-propylammonium perruthenate (TPAP, represented as [(n-Pr)₄N]RuO₄) at 80–110 °C is shown to proceed with selectivities of 72–91% at 55–80% alcohol conversion. The unsaturated alcohols, such as 9-decenol, 9-octadecenol and β-citronellol, give the corresponding unsaturated aldehydes without competing double bond attack. The time course of oxidation indicates a complex reaction mechanism. The results on oxidation of a test alcohol, t-Bu(Ph)CHOH, suggest that one-electron processes do not play an important role in the TPAP-catalysed aerobic oxidation of alcohols.     

Sugar allyltins in the synthesis of carbobicycles. Preparation of highly oxygenated enantiomerically pure decalins

Readily available unsaturated bicyclic ketones—obtained conveniently from sugar allyltins—are converted into highly oxygenated unsaturated decalins. The corresponding cis- and trans-diols resulting from oxidation of the double bond were obtained with 100% selectivity. Stereospecific introduction of nitrogen into the decalin system via azidation was also realized.     

Rotation about the exocyclic carbon-carbon double bond of amino dienes of the indolo[2,3-a]-and benzo[a]quinolizidine series

Quinolizidines containing an exocyclic double bond at C-2 (1,2) give on mild oxidation the amino dienes (3,4), as mixtures of geometric isomers with respect to the exocyclic double bond. The free enthalpy of activation for the rotation about the double bond has been estimated by NMR.     

Synthesis of novel phosphorus-containing sterically hindered phenols by the reaction of diphenyl (3,5-di-tert-butyl-4-oxocyclohexa-2,5-dienylidene)methylphosphonate with phenols

Diphenyl (3,5-di-tert-butyl-4-hydroxybenzyl)phosphonate was oxidized to the corresponding methylidenequinonoid derivative. The addition of phenols to the exocyclic double bond of this compound gave phosphonates with two phenol moieties.     

Beiträge zur Chemie der Pyrrolpigmente, 48. Mitt.

2,3-Dihydrobilatrienes-abc substituted analogous to the natural chromophor of phytochrome may exhibit diastereomerism at the exocyclic double bond of the unsaturated lactam ring. Their properties are comparable to the previouslystudied bilatriene-abc diastereomers. At the exocyclic double bond of the saturated lactam ring however, diastereomers could only be prepared for thermodynamic reasons. The spectroscopic properties of the various diastereomers of five compounds were recorded and are discussed with respect to their utility in structural studies of the natural pigment system.     

1,3-Dipolar addition of diazocyclopropane to eudesmane-type methylidene lactones and thermolysis of the resulting spiro-fused pyrazolines

Reactions of alanto-, isoalanto-, and alloalantolactones, which are unsaturated eudesmane-type lactones, with diazocyclopropane generated in situ from N-cyclopropyl-N-nitrosourea under the action of sodium methoxide proceed alike, are highly regio- and stereoselective, and always give spiro-fused pyrazolines via cycloaddition to the exocyclic double bond of the methylidene group of the lactone ring. Their thermolysis at 195?C210 °C results in elimination of molecular nitrogen, mainly yielding spiropentane-containing lactones. Minor thermolysis products (10?C12%) are isomeric 13-cyclopropyl lactones.     

Monoterpenoids dithiophosphates. Synthesis and biological activity

O,O-Dialkyldithiophosphoric acids adds at the double bond of the racemic camphene and (+)- limonene in the presence of Lewis acids in accordance with the Markownikoff rule with the formation of Sterpenyl esters of dithiophosphoric acids. The reaction with camphene is accompanied by the rearrangement of camphane structure to that of bornane. Addition of dithiophosphoric acid to (+)-limonene proceeds with the participation of the exocyclic double bond. Toxic and genotoxic properties of the monoterpenoid dithiophosphates were studied.     

2,2-Dimethyl-5-(5-R-2-furfurylidene)-1,3-dioxane-4,6-diones. 4. Synthesis,stereostructures, and properties of thiophene analogs

The reaction of 2-formylthiophenes with Meldrum's acid gave the corresponding thenylidenedioxanediones, which, in contrast to the furfurylidene derivatives, have an s-trans conformation of the mutual orientation of the thiophene ring and the exocyclic double bond. Thenyldioxanediones were synthesized by the selective hydrogenation of the exocyclic double bond.See [1] for Communication 3.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1338–1342, October, 1989.     

Stereoselective entry to beta-linked C-disaccharides using a carbon-Ferrier reaction

[structure: see text] The synthesis of unsaturated beta-linked C-disaccharides by the Lewis acid-mediated reaction of 3-O-acetylated glycals with monosaccharide-derived alkenes is described. Deprotection and selective hydrogenation of an exocyclic carbon-carbon double, in the presence of an endocyclic double bond, for representative targets is also illustrated.     

Thio-click approach to the synthesis of stable glycomimetics

Carbon-sulfur-bridged glycomimetics were prepared by free radical hydrothiolation of the exocyclic double bond of unsaturated sugars. Reaction between benzoyl-substituted pyranoid-exoglycal and a range of thiols including peptide, 1-thioglycerol and 1-thiosugar derivatives gave β-D-configured carbon-sulfur-linked glycoconjugates with full stereoselectivity. Addition of a panel of thiols to a 3-exomethylene-glucofuranose derivative also proceeded in a stereoselective manner and afforded a series of D-allo-configured 3-deoxy-3-C-S-bridged glycoconjugates.     

Conjugation and hyperconjugation in conformational analysis of cyclohexene derivatives containing an exocyclic double bond

The equilibrium geometry, ring-inversion pathway barriers for analogues of cyclohexene with an exocyclic double bond have been studied using the MP2/6-311 G(d,p) level of theory. The equilibrium conformation of the ring depends on conjugation between the endocyclic and exocyclic double bonds. Interactions between conjugated double bonds include the pi-pi conjugation and interactions between the lone pair of the heteroatom of the exocyclic double bond and the sigma-antibonding orbital of the endocyclic single bond. In the case of the tetrahydrocycles with double bonds separated by a methylene group the balance between the pi --> sigma* hyperconjugation interactions between the exocyclic double bond and the neighboring methylene group and the n --> sigma* interaction between the lone pair of the heteroatom and the sigma-antibonding orbitals of the C(sp(2))-C(sp(3)) bond determine the geometrical parameters of the ring. The character of the potential-energy surface around the saddle point depends on the position of the exocyclic double bond and the orientation of the hydrogen atom attached to the heteroatom of the V group of the periodic table in the tetrahydrocycles with double bonds separated by a methylene group.     

Intramolecular palladium-catalyzed cyclization of alkenylboronate prepared from hydroboration of terminal acetylene and its application to the stereoselective synthesis of (E)-doxepin

The hydroboration of 2-[(2-ethynylphenyl)methoxy]-1-iodobenzene with bis(pinacolato)diboron in the presence of palladium catalyst and followed by consecutive oxidative addition, cis-cyclocarbopalladation, and cis-β-elimination could give highly stereoselective exocyclic alkenylboronate ester. The following cross-coupling of the exocyclic alkenylboronate ester with 2-bromo-N,N-dimethylacetamide in the presence of palladium catalyst and followed by LAH reduction gives (E)-doxepin in fair yields.     

On the influence of chiral auxiliaries in the stereoselective cross-coupling reactions of titanium enolates and acetals

Titanium enolates from chiral N-propanoyl-1,3-thiazolidine-2-thiones containing bulky substituents at C4 turned out to be excellent platforms to get highly stereocontrolled cross-coupling reactions with acetals. Related oxazolidinethiones also afforded good results, but the corresponding oxazolidinones resulted completely unselective for such reactions, which proves that an exocyclic CS bond is essential to attain a synthetically useful stereocontrol.     

Efficient dual catalytic enantioselective diethylzinc addition to the exocyclic CN double bond of some 1,2,4-N-triazinylarylimines using polymer-supported chiral β-amino alcohols derived from norephedrine

Chiral N,N-dialkylnorephedrines and their corresponding copolymers were evaluated as chiral ligands for the enantioselective diethylzinc addition to the exocyclic CN double bond of some 4-arylideneamino-3-mercapto-6-methyl-4H-1,2,4-triazin-5-ones 2a-f. The use of a dual catalytic system (amino alcohol/halosilane) in the titled asymmetric reaction was examined. The enantioselective ethylation reaction has been successfully carried out in the heterogeneous system even at low temperature. The corresponding 4-(1-arylpropyl)amino-3-mercapto-6-methyl-4H-1,2,4-triazin-5-ones 4a-f were obtained in high yields with high enantioselectivities using chiral polymers (up to 91% ee), which are almost the same as those obtained from homogeneous analogues (up to 92% ee). The diethylzinc reagent neither opened the 1,2,4-triazinyl heterocyclic ring nor attacked the carbonyl or the thione groups of the 1,2,4-triazinyl heterocyclic ring and the addition reaction took place exclusively at the exocyclic electrophilic carbon atom yielding the C-ethylated products 4a-f. Reductive cleavage of the 1,2,4-triazinyl heterocyclic ring led smoothly to the corresponding primary aromatic amines 11a-f without significant loss of enantiomeric purity. A suggestion about the possible transition state for the addition reaction is also presented.     

Stereospecific functionalisations of iron carbonyl complexes of 5,6,7,8-tetrakis(methylene)bicyclo[2.2.2]oct-2-ene. Crystal and molecular structure of (C12H12)Fe2(CO)6

When the reaction between an excess of Fe₂(CO)₉ and the pentaene 5,6,7,8-tetrakis(methylene)bicyclo[2.2.2]oct-2-ene(I) is carried out in hexane/methanol the endo,exo-bis(tetrahaptotricarbonyliron) isomer (C₁₂H₁₂)Fe₂(CO)₆(IIa)is the major product. The structure of this complex has been determined by X-ray diffraction.The asymmetric positions of the two Fe(CO)₃ groups with respect to the roof-shaped organic skeleton was used to induce either stereo-specific functionalisation of the uncoordianted endocyclic CC double bond or stereo-and regiospecific functionalisation of one of the two coordinated s-cis-butadiene groups of the pentaene. Thus, hydroboration/oxidation of Ila gave the endo-exo-bis(tetrahaptotricarbonyliron)isomer of 5,6,7,8-tetrakis(methylene)bicyclo[2.2.2]octane-2-ol (IV). cis deuteration of the exocyclic double bond was achieved by treating IIa with D₂/PtO₂ in n-hexane.Protonation of IIa by HCl/AlCl₃/CH₂Cl₂ to give the η⁴-diene : η²-ene : η³-dienyl cationic complex Va, followed by quenching of Va with NaHCO₃/CH₃OH, resulted in a 1,4-addition of methanol to one coordinated s-cis-butadiene system. In contrast, quenching with NaOCH₃/CH₃OH resulted in the corresponding 1,2-addition of methanol. This gave the η⁴-1,3-diene : η⁴-1,4-diene complex VIIIa in which, suprisingly, one Fe(CO)₃ group is coordinated to two CC double bonds in gauche positions with respect to each other.     

Oxidation of olefins with 2-pyridineseleninic anhydride

2-Pyridineseleninic anhydride, prepared $\text{in situ}$ by oxidation of the corresponding diselenide with iodoxybenzene, is an efficient reagent for the conversion of olefins to unsaturated ketones with retention of the original position of the double bond. This reagent is, therefore, much more reactive towards olefins than benzeneseleninic anhydride. An explanation has been offered.     

Hydrogénolyse en phase liquide sur Pd/C des époxydes du carvomenthène et du limonène

Hydrogenolysis over Pd/C of cis and trans epoxides of carvomenthene and limonene give a mixture of hydrocarbons, secondary and tertiary alcohols, and ketones in proportions dependent upon the nature of the starting material. In the limonene epoxides, the extracyclic double bond plays an important role in the opening of the oxirane ring through a common unsaturated tertiary alcohol intermediate by double bond migration, hydrogenation of which leads to the products. For the carvomenthene epoxides the results are similar to those found in the 4-t-butyl series with competition between cis addition and trans addition of hydrogen. The presence of the isopropenyl group leads to slower reaction rates in comparison with t-butyl analogues.