Isomerization formates

Dealkylation, heteropoly compunds, 41 160-161, 170-174 Deamination, 27 259 Pd(NH3>/ ions, 39 142 Debye-Waller factor, 21 177 Decahydronaphthalenes conformation of, 18 17-19 isomeric, formation of in hydrogenation of naphthalenes, 18 23-20 rrans-Decalin... 

C is correct. The reaction produces only certain stereoisomeric products so it is stereoselective. Experiment 2 says that the products depend upon the isomeric formation of the reactants, so it is stereospecific. Any reaction that is stereospecific is also stereoselective, but the converse is not true. 

Figure 13. Partial hydrogenation. The partially hydrogenated intermediate (1) may iead to cis or trans unsaturated or saturated products. D—diene M—monoene S—saturate potentiaiiy isomerized. Formation of M is favored at a tow hydrogen concentration.

A deuterium label at the primary position could thus be used as a very sensitive probe for allyl isomerization. Formation of the primary a-allyl would be expected to scramble any initial configuration of the label to a random mixture of syn and anti deuterium. 

This can be understood by considering the all-/r<7 s structure of pyrrolidine 175 and the more thermodynamically stable 2,3-trans, 2,5-cis combination isomer 176, which features remove any benefit from isomerization. Formation of the latter isomer 176 also shows the same preference for a transition slate conformation in which the substituent a-to the nucleophilic centre occupies the axial position [99 and 143]. Similar chemistry can also be used for the stereoselective generation of perhydroindoles [e.g. 177J. 

Cyclohexanol conversion over H-ZSM-5 and H-boralite was also studied by Brabec et al. [188], who addressed the effects of concentration and strength of acid sites on catalytic activity. They found the number of acid sites needed increases in the order of dehydrogenation (formation of cyclohexene) < isomerization (formation of methylcyclopentene) < intermolecular reactions (formation of cyclohexane and methylcyclopentane). Even at reaction temperatures around 180 °C all products were observed. The intermolecular reaction pathway decreased in importance with TOS and practically vanished after 30 min. Deactivation, which is in general only slight on these catalysts. 

Any perturbation of the electron distribution in a molecule, such as produced by hydrogen bonding (either internal or external), isomerization, formation of charge transfer and other types of complexes, steric hindrance, etc., leads to a definite change in the spectral pattern. 

The reaction of (14) with 1-bromohex-l-yne gives a high yield of 3,6-dimethyl-pen tylidenecycloheptane. Cyclization of (15) with formic acid and boron trifluoride catalyst gives the isomeric formates (16), which are readily converted into 3,3,5-trimethylcycloheptanone diene (17) gives (18) as a minor product under similar conditions. ... 

The goal of this project is to determine the enthalpies of formation of cis- and trans-2-butene and to calculate the enthalpy of isomerization between them. 

Treatment of conjugated enyne systems, H C-C=C-CeC-CH-OR, with a suitable base in principle may give rise to 1,6-elimination of HOR with primary formation of the system C=C-C=C=C=C, which subsequently may undergo isomerization to a dienyne. ... 

Only relatively few examples of interesting target molecules containing rings are known. These include caryophyllene (E.J. Corey, 1963 A, 1964) and cubane (J.C. Barborak, 1966). The photochemical [2 + 2]-cycloaddition applied by Corey yielded mainly the /ranr-fused isomer, but isomerization with base leads via enolate to formation of the more stable civ-fused ring system. 

Isomerization of double bonds in vitamin D analogs such as calciferol by oxidation and reduction has been carried out via the formation of the tt-allylpalladium complex 334 with PdCl2(PhCN)2 in 70% yield, followed by hydride reduction to afford 335[295],... 

In an efficient diastereo-differentiative assembly of three components of norbornene, tv. v-alkenyl iodide, and KCN, the isomerization of the cis to the trans double bond takes place to give the coupled product 224. The isomerization is explained by the formation of the cyclopropane 222. its rearrangement to give a irans double bond in 223, and trapping with CN anion to give 224[168],... 

In the alkylative cyclization of the 1,6-enyne 372 with vinyl bromide, formation of both the five-membered ring 373 by exn mode carbopalladation and isomerization of the double bonds and the six-membered ring 374 by endo mode carbopalladation are observed[269]. Their ratio depends on the catalytic species. Also, the cyclization of the 1,6-enyne 375 with /i-bromostyrene (376) affords the endo product 377. The exo mode cyclization is commonly observed in many cases, and there are two possible mechanistic explanations for that observed in these examples. One is direct endo mode carbopalladation. The other is the exo mode carbopalladation to give 378 followed by cyclopropana-tion to form 379, and the subsequent cyclopropylcarbinyl-homoallyl rearrangement affords the six-membered ring 380. Careful determination of the E or Z structure of the double bond in the cyclized product 380 is crucial for the mechanistic discussion. 

Pd hydride. Subsequent enolate formation, double bond isomerization, and carbonylation give the butenolide 582. 

Acyl halides are intermediates of the carbonylations of alkenes and organic-halides. Decarbonylation of acyl halides as a reversible process of the carbo-nylation is possible with Pd catalyst. The decarbonylation of aliphatic acid chlorides proceeds with Pd(0) catalyst, such as Pd on carbon or PdC, at around 200 °C[109,753]. The product is a mixture of isomeric internal alkenes. For example, when decanoyl chloride is heated with PdCF at 200 C in a distillation flask, rapid evolution of CO and HCl stops after I h, during which time a mixture of nonene isomers was distilled off in a high yield. The decarbonylation of phenylpropionyl chloride (883) affords styrene (53%). In addition, l,5-diphenyl-l-penten-3-one (884) is obtained as a byproduct (10%). formed by the insertion of styrene into the acyl chloride. Formation of the latter supports the formation of acylpalladium species as an intermediate of the decarbonylation. Decarbonylation of the benzoyl chloride 885 can be carried out in good yields at 360 with Pd on carbon as a catalyst, yielding the aryl chloride 886[754]. 

Various terminal allylic compounds are converted into l-alkenes at room temperature[362]. Regioselective hydrogenolysis with formate is used for the formation of an exo-methylene group from cyclic allylic compounds by the formal anti thermodynamic isomerization of internal double bonds to the exocyclic position[380]. Selective conversion of myrtenyl formate (579) into /9-pinene is an example. The allylic sulfone 580 and the allylic nitro compound... 

As a further application of the reaction, the conversion of an endocyclic double bond to an c.xo-methylene is possible[382]. The epoxidation of an cWo-alkene followed by diethylaluminum amide-mediated isomerization affords the allylic alcohol 583 with an exo double bond[383]. The hydroxy group is eliminated selectively by Pd-catalyzed hydrogenolysis after converting it into allylic formate, yielding the c.ro-methylene compound 584. The conversion of carvone (585) into l,3-disiloxy-4-methylenecyclohexane (586) is an example[382]. 

An active catalytic species in the dimerization reaction is Pd(0) complex, which forms the bis-7r-allylpalladium complex 3, The formation of 1,3,7-octa-triene (7) is understood by the elimination of/5-hydrogen from the intermediate complex 1 to give 4 and its reductive elimination. In telomer formation, a nucleophile reacts with butadiene to form the dimeric telomers in which the nucleophile is introduced mainly at the terminal position to form the 1-substituted 2,7-octadiene 5. As a minor product, the isomeric 3-substituted 1,7-octadiene 6 is formed[13,14]. The dimerization carried out in MeOD produces l-methoxy-6-deuterio-2,7-octadiene (10) as a main product 15]. This result suggests that the telomers are formed by the 1,6- and 3,6-additions of MeO and D to the intermediate complexes I and 2. 

Carboxylic acids react with butadiene as alkali metal carboxylates. A mixture of isomeric 1- and 3-acetoxyoctadienes (39 and 40) is formed by the reaction of acetic acid[13]. The reaction is very slow in acetic acid alone. It is accelerated by forming acetate by the addition of a base[40]. Addition of an equal amount of triethylamine achieved complete conversion at 80 C after 2 h. AcONa or AcOK also can be used as a base. Trimethylolpropane phosphite (TMPP) completely eliminates the formation of 1,3,7-octatriene, and the acetoxyocta-dienes 39 and 40 are obtained in 81% and 9% yields by using N.N.N M -tetramethyl-l,3-diaminobutane at 50 in a 2 h reaction. These two isomers undergo Pd-catalyzed allylic rearrangement with each other. 

Anilines react with ct-haloacetophenones to give 2-arylindoles. In a typical procedure an W-phenacylaniline is heated with a tw o-fold excess of the aniline hydrobromide to 200-250°C[1]. The mechanism of the reaction was the subject of considerable investigation in the 1940s[2]. A crucial aspect of the reaction seems to be the formation of an imine of the acetophenone which can isomerize to an aldimine intermediate. This intermediate apparently undergoes cyclization more rapidly (path bl -> b2) than its precursor (Scheme 7.3). Only with very reactive rings, e.g, 3,5-dimethoxyaniline, has the alternative cydiz-ation (path al a2) to a 3-arylindole been observed and then only under modified reaction conditions[3],... 

The first identified complexes of unsubstituted thiazole were described by Erlenmeyer and Schmid (461) they were obtained by dissolution in absolute alcohol of both thiazole and an anhydrous cobalt(II) salt (Table 1-62). Heating the a-CoCri 2Th complex in chloroform gives the 0 isomer, which on standirtg at room temperature reverses back to the a form. According to Hant2sch (462), these isomers correspond to a cis-trans isomerism. Several complexes of 2,2 -(183) and 4,4 -dithiazolyl (184) were also prepared and found similar to pyridyl analogs (185) (Table 1-63). Zn(II), Fe(II), Co(II), Ni(II) and Cu(II) chelates of 2.4-/>is(2-pyridyl)thiazole (186) and (2-pyridylamino)-4-(2-pyridy])thiazole (187) have been investigated. The formation constants for species MLr, and ML -" (L = 186 or 187) have been calculated from data obtained by potentiometric, spectrophotometric, and partition techniques. 

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