Mercury(II) and palladium(II) salts have found broad applications as catalysts for [3,3]-sigmatropic rearrangements leading to formation of CO, CN, CS, and CC σ bonds. Increases in reaction rate are often very large (1010 – 1014 at 1 M catalyst concentration) and allow many previously difficult transformations to be conducted at or near room temperature, often with attendant increases in stereoselectivity and decreases in by-product formation. The mechanism of these catalyzed transformations is briefly discussed, and evidence is summarized to suggest that many follow a cyclization-induced rearrangement mechanism.

Mercury(II)‐ and Palladium(II)‐Catalyzed [3,3]‐Sigmatropic Rearrangements [New Synthetic Methods (46)]

2-Allylphenols react with carbon monoxide and hydrogen in the presence of catalytic quantities of a cationic palladium(II) complex [(PCy3)2Pd(H)(H2O)]+BF4- or palladium acetate and 1,4-bis(diphenylphosphino)butane, affording five- or seven-membered ring lactones (bicyclic, tricyclic, and pentacyclic) as the principal products, often in excellent yields. Use of 2-aminostyrenes as reactants and catalytic quantities of palladium acetate and tricyclohexylphosphine, affords five-membered ring lactams in high yield and selectivity. Bicyclic and tricyclic heterocycles containing six-membered ring lactams can be synthesized from the reaction of 2-allylanilines with CO/H2 using the catalytic system Pd(OAc)2/PPh3, while use of 1,4-bis(diphenylphosphino)butane instead of PPh3 in the latter process results in the formation of the seven-membered lactams benzazepinones in good yield. The regiochemical control depends on the nature of the palladium catalyst, the relative pressures of the gases, and the solvent.

Regioselective Palladium(II)-Catalyzed Synthesis of Five- or Seven-Membered Ring Lactones and Five-, Six- or Seven-Membered Ring Lactams by Cyclocarbonylation Methodology

Untersuchungen über aromatische Amino‐Claisen‐Umlagerungen

New catalytic systems have been found which effect the isomerization of α-acetylenic alcohols to the corresponding α, β-unsaturated carbonyl compounds with high efficiency. These are combinations of silylvanadates with silanols or silanediols.

The Rearrangement of α‐Acetylenic Alcohols to α, β‐Unsaturated Carbonyl Compounds by Silylvanadate Catalysts

Allyl aryl ethers which have no strongly electron attracting substituents undergo a charge-induced [3 s, 3 s] sigmatropic rearrangement in the prescence of 0.7 mole boron trichloride in chlorobenzene at low temperature, to give after hydrolysis the corresponding o-allyl phenols (Tables 1 and 2). The charge induction causes an increase in the reaction rate relative to the thermal Claisen rearrangement of ∼1010. With the exception of allyl 3-methoxyphenyl ether (5), m-substituted allyl aryl ethers show similar behaviour (with respect to the composition of the product mixture) to that observed in the thermal rearrangement (Table 3). The rearrangement of allyl aryl ethers with an alkyl group in the o-position, in the prescence of boron trichloride, yields a mixture of o- and p-allyl phenols, where more p-product is present than in the corresponding product mixture from the thermal rearrangement (Table 4). This ‘para-effect’ is especially noticeable for o-alkylated α-methylallyl aryl ethers (Table 5 ).



With boron trichloride, 2,6-dialkylated allyl aryl ethers give reaction products which arise, in each case, from a sequence of an ortho-Claisen rearrangement followed by a [1,2]-, [3,3]- or [3,4]-shift of the allyl moiety (Tables 6 and 7). Ally1 mesityl ether (80), with boron trichloride, gives pure 3-ally1 mesitol (95). From phenol, penta-ally1 phenol (101) can be obtained by a total of five O-allylations followed by three thermal and two boron trichloride-induced rearrangements.



The sigmatropic rearrangements of the ethers studied, using D- and 14C-labelled compounds, are collected in scheme 2; only the reaction steps indicated by heavy arrows are of importance.



With protic acids, there is a [3,3]-shift of the allyl group in 6-allyl-2,6-disubstituted cyclohexa-2,4-dien-l-ones, while with boron trichloride the [3,3]-reaction is also observed along with the much less important [1,2]- and [3,4]-transformations (Table 8). 4-Allyl-4-alkyl-cyclohexa-2,5-dien-1-ones give only [3,3]-rearrangements with boron trichloride (Table 9). As expected, the naphthalenone 112, which is formed by allowing boron trichloridc to react for a short time with allyl (1-methyl-2-naphthyl) ether (111), undergoes only a [3,4] rearrangement (Scheme 3).



Representations of how, in our opinion, the complex behaviour of allyl aryl ethers and allyl cyclohexadienones under the influence of boron trichloride, can be rationalized are collected together in Schemes 4 and 5.



In the last part of the discussion section, the steric factors leading to the appearance of the ‘para-effect’, are dealt with (Scheme 6).

Umlagerung von Allyl‐aryläthern und Allyl‐cyclohexadienonen mittels Bortrichlorid

N-Allyl-2-methylaniline (12) forms on heating at 140° in xylene in the presence of zinc chloride 2-allyl-6-methylanline (19) as major compound and 4-allyl-2-methylaniline (20) as well as 2,7-dimethyl-indoline (21) as minor products. Compound 21 is also formed when 19 is heated in the presence of zinc chloride (scheme 2). That 19 arises from a charge-induced [3s, 3s] sigmatropic rearrangement of 12 – and 20 from two consecutive [3s, 3s]-sigmatropic transformations – follows from the reaction of N-crotyl-2-methylaniline (13) in the presence of zinc chloride at 140°. 2-(1′-Methylallyl)-6-methylaniline (22) and 4-crotyl-2-methylaniline (23) are formed exclusively. Small amounts of 2,3,7-trimethyl-indoline (24) and 2-(cis- and trans-1′-methyl-propenyl)-6-methylaniline (cis- and trans-25) are observed as by-products. Compound 24 arises from 22 in the presence of zinc chloride (scheme 3). Similar results are obtained when N-allyl and N-(2′-methylallyl)-N-methyl-aniline (14 and 15, respectively) are heated in the presence of zinc chloride. Whereas 14 gives nearly exclusively 2-allyl-N-methyl-aniline (28) and only small amounts of the corresponding 1, 2-dimethyl-indoline (29) and of 2-(cis- and trans-propenyl)-N-methyl-aniline (cis- and trans-27), 15 forms comparable amounts of 2-(2′-methylallyl)-N-methyl-aniline (30), 1,2,2-trimethyl-indoline (31), and 2-isobutenyl-N-methyl-aniline (32) (scheme 4). Compound 30, and also 32, are transformed into 31 on heating in the presence of zinc chloride.



Charge-induced aromatic amino-Claisen rearrangements are also observed when N-allylated anilinium tetraphenylborates are heated at 100–105° in hexamethyl phosphoric acid triamide. Thus, N-allyl- and N-crotyl-N, N-dimethyl-anilinium tetraphenylborate (16 and 17, respectively) yield 2-allyl- and 2-(1′-methylallyl)-N,N-dimethyl-aniline (33 and 34, respectively) besides small amounts of N, N-dimethyl-aniline. N-Cinnamyl-N, N-dimethyl-anilinium tetraphenylborate (18) gives, besides appreciable amounts of N,N-dimethyl-aniline, a mixture of 2-(1′-phenylallyl)-,2-cinnamyl-, and 4-cinnamyl-N, N-dimethyl-aniline (35, 36, and 37, respectively) in which the first two compounds predominate.

Zinkchloridkatalysierte, thermische Umlagerungen von N‐Allyl in C‐Allyl‐aniline; ladungsinduzierte, aromatische Amino‐Claisen‐Umlagerungen

The tosylhydrazones of 4-allyl- and 4-crotyl-4-methyl-cyclohexa-2, 5-dien-l-one (14 and 15) rearrange in the presence of acid to yield the corresponding 2-allyl- and 2-α-methylallyl-hydrazines 17 and 18, respectively. A similar behaviour is shown by the tosylhydrazone of 2-allyl-2-methyl-cyclohexa-3, 5-dien-1-one (16). 16 could not be isolated. The observed acidcatalysed [3 s, 3 s]-sigmatropic rearrangement of the tosylhydrazones can be regarded as a rearrangement of the dienimine-aniline type.

Säurekatalysierte Umlagerung von Allyl‐cyclohexadienon‐tosyl‐hydrazonen: Beispiel einer Dienimin‐Anilin‐Umlagerung

Das Hydrazon (I), das aus dem entsprechenden Keton und p-Toluo1sulfonsaurehydrazid erhalten wurde (Ausbeute 21%), erfahrt in Methylenchlorid eine saurekatalysierte Umlagerung zu dem aromatischen Isomeren (II) (70,5%), dessen Identitat durch Abbaureaktionen bestatigt wurde.

M. Schmid

Papers

Zinkchloridkatalysierte, thermische Umlagerungen von N‐Allyl in C‐Allyl‐aniline; ladungsinduzierte, aromatische Amino‐Claisen‐Umlagerungen

Säurekatalysierte Umlagerung von Allyl‐cyclohexadienon‐tosyl‐hydrazonen: Beispiel einer Dienimin‐Anilin‐Umlagerung

Saeurekatalysierte umlagerung von allyl‐cyclohexadienon‐tosylhydrazonen, beispiel einer dienimin‐anilin‐umlagerung