Unexpected products

On account of the catalytic properties of transition metals imexpected products are frequently obtained in reactions involving their organometallic compoimds. For example the reaction of cyclohexene with palladium chloride probably gives initially the expected olefin complex, which is unstable, however, and loses a hydrogen atom to yield a Tr-onyl complex. 

iron pentacarbonyl isomerizes m-substituted conjugated dienes giving products derived from the trans-isomer. This may occur since the repulsive interaction between substituents and the metal would be less in this configuration, e.g. 

Oligomerization of olefins or acetylenes can also occur in their reactions with transition metal compounds. Treatment of rutheniimi trichloride in 2-methoxyethanol with butadiene at 90°C yields the complex 6.7 the structure of which has been determined by X-ray diffraction. (Related reactions involving bis-ir-allyl nickel and butadiene arc discussed in Chapter 10.) 

Acetylenes espedally are prone to give unusual reactions, many of which involve oligomerization of the ligand. Examples of some types of products which can be formed in their reactions with compounds of transition metals are given in Table XVIII (Chapto 9). 

Most unexpected is the isolation in low (O S %) yield of a black complex FesC(CO)x5 from the reaction of Fc3(CO)i2 with 1-pentyne. The X-ray crystal structure shows a formally pentaco-ordinate carbon atom located slightly below the plane of the four iron atoms and approximately equidistant from all five iron atoms, 6.8. 

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In this phase of the toller selection process, we assume the long list became a short list and now one or more candidate tollers from the short list will be given an opportunity to prepare a commercial bid. This by no means indicates the short listed tollers are perfect. There may be deficiencies that need to be corrected in concert with the client. With proper effort, one will be successful and be engaged for the toll. Sometimes it is appropriate to decide on a backup toller, as complications can develop that prevent the primary candidate from executing the project as originally planned, due to an incident in their plant, departure of key personnel, or unexpected production demands on the toller. 

In 1955, Hurd and Mori first described the preparation of 1,2,3-thiadiazole as an unexpected product from the reaction of the hydrazone 5 and thionyl chloride. The authors were attempting to prepare the six membered anhydride 7 in an analogous manner to the 5-membered anhydride 9, prepared from 8 using thionyl chloride. However, when the hydrazone 5 and thionyl chloride were mixed and heated at 60°C for 1 hour followed by cooling, the thiadiazole acid 6 precipitated out and was isolated by filtration. This serendipitous discovery led to a significant advance in the synthesis of thiadi azoles. 

Boron trifluoride etherate, is also a good catalyst for this hydride transfer to chalcone. Unlike triphenylmethyl perchlorate, however, chalcone is able to enter Michael additions with the 1,5-diketone followed by eliminations leading to unexpected products, e.g., 3-benzyl-2,4,6-triphenylpyrylium from 2-carbethoxy-l,3,5-tri-phenylpentane-l,5-dione and chalcone the benzyl group originates from chalcone, the elimination product being ethyl benzoylacetate. ... 

Virtually any aldehyde or ketone and any CH-acidic methylene compound can be employed in the Knoevenagel reaction however the reactivity may be limited due to steric effects. Some reactions may lead to unexpected products from side-reactions or from consecutive reactions of the initially formed Knoevenagel product. 

These reactions can give unexpected products. When Hg[Co(CO)4]2 reacts with Hg(CN)2 in alkaline MeOH the cluster Hg,C0fc(CO),g forms. ... 

Attempted deoxygenation of several fT-aryl thiono carbonates gave the unexpected product shown. In contrast, the corresponding a-isomers gave the desired deoxygenation product. Account for the formation of the observed products, and indicate why these products are not formed from the a-stereoisomers. 

In acetic acid, or aqueous acetone with subsequent treatment with acetic anhydride, the esters (196 R=4-Me0 or 4-MeS) give rise to the expected esters(197) or (198). For the 4-chlorophenyl derivative, a mixture of the unexpected products (199, 200 Ar=4-chlorophenyl) was obtained. The unsubstituted compound (196 R=H) gave only (199) in aqueous acetone, but (200) in acetic acid. The postulated mechanism tor such a rearrangement centres around pseudophosphonium and-or phosphorane... 

Some 2,3-diazabicyclo[2.2.1]heptene derivatives, for example, 175, with an aryl iodide and allyltributyltin in the presence of [Pd(allyl)Cl]2 in toluene provide unexpected products 176. It is interesting to note that aryl iodide is recovered almost completely but no reaction can be observed in its absence. When the aryl iodide is replaced by a Lewis acid, good yields of 176 are obtained. The reaction is very slow in toluene, but in ionic liquid [bmim]PF6 the reaction rate is significantly enhanced (Equation 21) <2005SL2273>. 

The co-condensation reactions described above have led to the formation of interesting new compounds and sometimes very unexpected products. The nature of the products formed for example in the osmium atom experiments indicate high degrees of specificity can be achieved. However, the detailed mechanisms of the co-condensation reactions are not known. It seems most likely that in all cases the initial products formed at the co-condensation temperature are simple ligand-addition products and that the insertion of the metal into the carbon-hydrogen bond occurs at some point during the warming up process. In support of this hypothesis we note the virtual absence of any... 

The authors reported that fucosterol (56) and isofucosterol (57) were transformed not only to desmosterol (34) and cholesterol (I), but also to 24-methylenecholesterol (36) [49]. The unexpected production of 24-methylenecholesterol... 

The decarbonylations, which do not appear to be affected by light, are reasonably selective with aromatic aldehydes, yielding the expected product however, significant amounts of other products are obtained with non-aromatic substrates (e.g. cyclohexane-aldehyde gives methylcyclopentane and small amounts of n-hexane, as well as the expected cyclohexane and cyclohexen-4-al gives both cyclohexene and cyclohexane). Indeed, the unexpected products perhaps provided a major clue to an understanding of the reaction mechanism(s) involved. 

These cycloadducts, at their most elementary level, are excellent intermediates for the synthesis of 3-substituted furan derivatives. For example, Kawanisi and coworkers reported a synthesis of perillaketone 174 in which the critical step was a Paterno-BUchi photocycloaddition between furan and 4-methylpentanal in the presence of methanesul-fonic acid (Scheme 39)82. This reaction furnished two initial photoadducts, 172 and 173. The unexpected product 173 presumably arises from a Norrish Type II cleavage of 4-methylpentanal to give acetaldehyde, and subsequent cycloaddition with furan. The desired cycloadduct 172 was then converted uneventfully to 174 via acid-catalyzed aromatization and oxidation. 

An unexpected production of 2,4,6-triphenyl-l, 3,5-triazine in the electroreduction of 3,4-diphenyI-l,2,5-thiadiazole 1-oxide has been reported . Synthesis of 1,3-diyne derivatives of 2,4-diamino-l,3,5-triazine, 9a and 9b, has been accomplished by reaction of biguanidine with mono- and di-esters 8a and 8b, respectively <00T1233>. 

Reactions of 1,2-diazepines with nitrile oxides are sometimes difficult to elucidate because they give mixtures (328) or unexpected products. Thus, reactions of 3-methyl- and 3,7-dimethyl-1,2-diazepines with mesitonitrile oxide leads to 5,10-dioxa-l,2,4,ll-tetrazatricyclo[7,3,l,02,6]trideca-3,7,l 1-triene derivatives 162 (R = H, Me, respectively) (329). Such structures were determined by X-ray diffraction studies (330). 

In this manner, the Ag salt of trinitromethane is involved in cascade reactions with branched alkyl halides to give unexpected products. 

The addition of B-alkylcatecholboranes to quinones has recently been investigated [85]. Good yield of the expected conjugate addition product are obtained with primary and most secondary radicals (Scheme 34, Eq. 34a). However, hindered secondary radicals and tertiary alkyl radicals afford an unexpected product resulting from a radical addition to the oxygen atom of the quinone (Eq. 34b). 

The next homologues are 1- and 2-butyne, where similar isomerizations have been observed [20] a recent report describes the reaction on a basic, alkali metal-exchanged zeolite [21]. As an unexpected product, an allene was obtained in reactions with hydrogen and a samarium catalyst [16, 22]. 

The competition of Claisen rearrangement and [l,5]-acetyl shift upon thermal treatment of allyl aryl ether 356 resulted in a mixture of the expected Claisen product 357 and its isomer 358 (equation 129)184. It was assumed that the usual Claisen rearrangement (Section IV.E.l) resulted in an equilibrium with the intermediates of successive [3,3]-sigmatropic shifts. The cyclohexa-2,4-dienones 359 and 360 formed leave this equilibrium cycle due to enolization to form the Claisen product 357 or because of [l,5]-shift followed by enolization give the unexpected product 358 (equation 130). 

Both acridone and dibenzo[6,/]azepine produce unexpected products (Scheme 7.39) when reacted with dimethylvinylidene carbene (7.1.18.A). Acridone reacts initially at the nitrogen atom to produce the 10-(3,3-dimethylallenyl) derivative (13%) and a pyrroloacridone (10%) which, if the structure is correct, could be derived from the allene by sigmatropic shifts [16]. The dibenzoazepine reacts as expected to produce a cyclopropyl derivative but, under the reaction conditions, the adduct rearranges spontaneously to yield a 1,6-methanodibenzo[b,/]cyclo-prop [J]azepine, the structure of which was confirmed by X-ray crystallography [17]. 

Aside from the mixture of species 4 resulting from disproportionation, the reaction of LAH with highly hindered alcohols (or phenols) may lead to unexpected products. Refluxing a THF solution of lithium bis(2,6-di-/-butylphe-noxy)aluminum hydride (7) resulted in the reduction of THF to 1-butanol (41). 

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