Rearrangement derivatives

An interesting annelation reaction of allene-derived 13-dipoles with 3-(IV-aryliminomethyl)chromones 38 affords, in fair yields, after [4 +3] cycloaddition and a subsequent cascade of rearrangements, derivatives of the novel iV-aryl-2,3-dihydro-4-ethoxycarbonylchromano[2,3-h]azepin-6-one system 39 (for example, R = Me, R1 = Cl) (Scheme 9). In the initial cycloaddition, the substituted chromone acts as an azadiene moiety <00OL2023>... 

The various, complex, cascade reactions described above converted simple saturated and aromatic heterocycles into polycyclic pentathiepins and their chlorinated and rearranged derivatives this strikingly illustrates the extensive reactivity of S2CI2 and its complexes with bases, particularly DABCO. This reactivity encompassed dehydrogenation of tetrahydroaromatics, chlorination and sulfuration of aromatics and their conversion into SSCl derivatives. 

Using 5(3,6(3-epoxycholestan-3(3-yl acetate as substrate, other solvents were also screened in this reaction and it was observed that using MeN02, a solvent with higher dielectric constant, the preferential formation of the backbone rearranged derivative occurred, but the Westphalen-type compound was also formed (Scheme 31). 

Mao S-C, Guo Y-W (2006) A Laurane Sesquiterpene and Rearranged Derivatives from the Chinese Red Alga Laurencia okamurai Yamada. J Nat Prod 69 1209... 

If the migrating carbon is part of a ring system, the Stevens rearrangement products arise by means of a ring expansion. For example, treatment of pyrrolinium salt 9 with base led to the isolation of a crystalline pyrrolinium ylide that gave the rearranged derivative 10 on further heating.12 Similarly, ylide 11 was smoothly transformed into amino ketone 12.13... 

CcHiimon by-products in these reactions are (methylthio)methyl ethers (3) formed by a Pummerer rearrangement which occurs via an alternative breakdown of (2), as shown in Scheme 3. The proportion of the Pummerer rearrangement derived product varies with the electrophilic activator used. 

Treatment of benzaldehyde oxime ether (166) with butyllithium (pentane/-10 C) demonstrates the complexity of the reaction (Scheme 32) as the desired alkoxyamine (167 R = Bu) is accompanied by other oxime-derived side products" (entry 1, Table 12). Selectivity is reagent/solvent dependent as allyl Grignard (ether)," allylzinc bromide (THF)," and butyllithium (THF)" treatment produce predominantly amine (171 R = allyl) (the Beckmann rearrangement derived product), alkoxyamine (167 R = allyl) (the oxime addition product) and ketone (169 R = Bu) (the nitrile-derived pro ct), respectively (entries 2-4, Table 12). 

From a practical standpoint, in metaphase plates, two types of chromosomal damage can be observed—simple chromosome breaks and complex structural rearrangements (Fig. 1). The importance of structural rearrangements derives from the fact that stable morphologic aberrations can only... 

Treatment of l,6-anhydro-3,4-dideoxy-P-D-/Areo-hex-3-enopyranoside with thion dhloride in pyridine gave the 2,3-unsaturated D-erythro-ctAoride 27 which, on reaction with O or S nucleophiles, gave rearranged derivatives 28. ... 

The concept of silyl enol ether synthesis via / -elimination from a Brook rearrangement-derived carbanion also appeared in Wicha s studies on additions of 1-phenyl-l//-tetrazol-5-yl (PT) sulfonyl anions to acyl silanes. When PT sulfone 34 was deprotonated in the presence of acyl(triphenyl)silane, ketone 36 was isolated in good yield after hydrolysis of the silyl enol ether intermediate 35. The mechanism involved addition of the... 

On the other hand, a substrate with an axial halogen has a semi-U geometry. In the presence of a base, the developing carbanion (in the transition state), which can initially be described by an sp orbital, does not have the appropriate stereochemistry to react with the axial C-Cl bond (sec Scheme 7). In an aprotic medium the carbanion carbon has rehybridized into a p orbital stabilized by overlap with the carbonyl p orbitals, and the formation of a zwitterion is observed. Cyclization of the latter will lead to the two isomeric cyclopropanones 14 and 15, which will yield the two rearranged derivatives 14a and 15a by ring opening. 

Fort was the first to obtain evidence for the zwitterion by studying the behavior of chlorodibenzylketone 29c under Favorskii rearrangement conditions. In the presence of a weak base such as 2,6-lutidine in MeOH 29c yields the methoxydibenzylketone 30. With a stronger base such as EtONa in EtOH, the rearranged derivative 31 is obtained. On the other hand, in the presence of lutidine and furan in DMF, Fort isolated the adduct 33. The reactivity of compound 29c is similar to that of 2-chlorocyclohexanone (27) (Table 4), which forms a symmetrical intermediate. The similarity in reactivity is confirmed by the isolation of adduct 33, which provides evidence for the intervention of a symmetrical delocalized intermediate which is most likely to be the zwitterion 32, stabilized by two phenyl groups. 

Although names and properties of thousands of hydrocarbons and their variously oxidized and rearranged derivatives have been compiled and catalogued (variously complete catalogues that are incomplete when published), the exact number of terpenes (Cio), sesquiterpenes (C15), diterpenes (C20), sesterpenes (C25), triterpenes (C30), carotenoids (C40), and varieties of rubber (e.g., laytex and gutta-percha) is unknown. Similarly, tomes have been written on the subject, and the discussion of these compounds here will end with an introduction to the triterpenes because these serve as sources of steroids (animal) and sterols (plants). 

Sterols and Related Products - The Westphalen rearrangement of some JP-substituted-bp-acetoxy-5Q -hydroxycholestanes has been studied and the products and kinetics shown to be dependent on the nature of the 5-substituent. The conformations of the products were studied and in the case of the Westphalen-Lettre derivatives it was shown that ring B is in the boat conformation. The boron trifluoride catalyzed cleavage of 30 -acetoxy-4a,5-epoxy-5Ci -cholestane afforded the expected backbone rearrangement products containing a 15(17) doable bond." A similar experiment with 5Q -acetoxy-5,ba-epoxy-5o -cholestane yielded some of the rearranged derivative XW after a reaction time of 25 seconds, along with the e q)ected isomer " ... 

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