Rearrangements 1.3- alkyl

In 1995, Mioskowski and co-workers reported a new carbenoid 1,2-alkyl rearrangement of a-hydroxy-substituted cyclopentene and cyclohexene oxides treatment of such systems with 3 equiv of an organolithium resulted in the formation of two products, as exemplified by the synthesis of dihydrojasmone and its regioisomer 99 (Scheme 44) <1995JA12700>. 

Addition of the diazoalkane nucleophile is followed by an reaction with ring-closure or a homologous ketone is formed with a 1,2-alkyl rearrangement (shift). Spirooxiranes are produced from cyclic ketone derivatives with diazomethane (Eq. 86). ... 

Wagner-Meerwein type 1,2-alkyl rearrangement was employed to access (-)-trigonoliimine C from the same hydroxyindolenines intermediate (Scheme 14.7) [67]. Heating... 

It has been pointed out that there are two distinct stereochemical orientations (referred to here as syn and anti) of the C-H bond undergoing a 1,3-hydrogen elimination from a carbonium ion (797). However, since 1,2-alkyl rearrangement is likely to be more rapid than 1,3-hydrogen elimination, distinguishing between these two modes of elimination becomes difficult. Nevertheless, there does appear to be a stereochemical requirement of co-planarity, i.e. 1,3-elimination is evidently unfavorable from a skew conformation. 

C-Alkylations may be discussed under the headings of alkene reactions and A/-alkyl rearrangements. The isopropylation of benzene and naphthalene are two important examples of alkylation with alkenes (see Alkylation). Manufacture of j butylaniline, by heating /V-butylaniline with 2inc chloride, typifies the rearrangement reaction appropriate to and higher alkyl derivatives. 

H-Azepin-2-one, 3-acetyl-synthesis, 7, 542-543 3/f-Azepin-2-one, 7-acetyl-synthesis, 7, 542-543 3H-Azepin-2-one, 3-acyl-rearrangements, 7, 505 3/f-Azepin-2-one, 3-acyl-2-alkoxy-formation, 7, 542-543 3H-Azepin-2-one, 1-alkyl-rearrangements, 7, 505 3/f-Azepin-2-one, N-alkyl-synthesis, 7, 511 Azepinones... 

Symmetrical ketones can be prepared in good yields by the reaction of organo-mercuric halides with dicobalt octacarbonyl in THF, or with nickel carbonyl in DMF or certain other solvents. The R group may be aryl or alkyl. However, when R is alkyl, rearrangements may intervene in the C02(CO)g reaction, though the Ni(CO)4 reaction seems to be free from such rearrangements. Divinylic ketones... 

Shimizu and co-workers reported that thermal decomposition of A4-thiabenzenes ylides afforded both thienofuran and thiophene derivatives in addition to the expected alkyl-rearranged products. A plausible mechanism was proposed with a [3.1.0] bicyclic sulfonium salt 9 as the key reactive intermediate <2001J(P1)2269>. Warren and co-workers, in their study of stereospecific phenysulfanyl migrations, found that [l,4]-sulfanyl participation could compete with the usual [l,2]-sulfanyl participation <1999SL1211>. Rearrangement of alcohol 18 with TsCl in pyridine gave an inseparable mixture of isomeric chlorides, 19 and 20, in a ratio of 52 48, as shown in Equation (3). 

The mechanisms of the (>-(acyloxy) alkyl, and later the (3-(phosphaloxy)alkyl rearrangements have been the subject of considerable effort by computational... 

Thermal decomposition of the benzoyl-substituted A -thiabenzenes 490a and 490b affords alkyl-rearranged 2-(4-bromophenyl)-3a,6a-dihydro-3,6,6a-trimethylthieno[3,2-3]furan 491a and 2-(4-bromophenyl)-3-ethyl-3a,6a-dihydro-6,6a-dimethylthieno[3,2-3]furan 491b (Scheme 61). A plausible mechanism for the formation of these products is also discussed <2001J(P1)2269>. 

In a synthesis of aspidospermidine [232] an alkylative rearrangement was employed to gain entry into the pentacyclic skeleton. 

Organoaluminum reagents have also been employed for alkylative rearrangement, but use of Grignard reagents permits greater flexibility. Reagents of the type RLi or RZnX are either ineffective or less satisfactory. 

In this context, it is worth mentioning that the C(l )-substituted C(2 ) radical undergoes rapid P-(acyloxy) alkyl rearrangement [reaction (261)], whereby a C(l )-type radical is also formed (Gimisis et al. 1995,1998). 

Photolysis of (Co)CH2Ph results in an unusual cobalt-to-carbon alkyl rearrangement (Scheme 8.19).108... 

Friedel-Crafts alkylation, rearrangements, multiple alkylation, fails with deactivated rings... 

Neutral and cationic homoleptic (see Homoleptic Compound) tnngsten-isocyanide complexes W(CNR)6 and [W(CNR)y] + (R = alkyl, aryl) are known, and W(CO)e (CNR) (n=l-3) complexes may be prepared from W(CO)6 and excess isocyanide in the presence of catalytic amounts of C0CI2 or PdO. Iso-cyanides are isoelecfronic with CO and also insert into the W-R bonds of alkyl complexes (see Alkyl Complexes). For instance, the alkyl-nitrosyl complexes Cp W(NO)(X)(CH2Bfr) (X = NHBfr, OBfr) react with CNBu to afford -iminoacyl complexes, and the isocyanide complexes, Cp W(CO)2(Me)(CNR) (10, R = alkyl), rearrange to afford either -iminoacyl Cp W(CO)2( -MeCNR)(ll) or ij -l-azaallyl Cp W(CO)2( -CH2CHNR) (12) derivatives, depending upon the reaction conditions (equation 4). ... 

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