Rearrangements 1.2- methyl

Compared to the parent system 3a, the barrier for formation of 3d is the highest in this series whereas the formation of 3b should be the most facile according to our computations. Although the reactions of carbenes la-c are initiated photochemically, the observed reactivity seems to be in line with the computed ground state properties. Thus, while methyl substitution in 3-and 5-position inhibits the vinylcarbene-cyclopropene rearrangement, methyl substitution in 2- and 6-position has the opposite effect. 

Organoaluminum-promoted Beckmann rearrangement/methylation of cyclohexanone oxime mesylate, followed by allylation of ketimine 40a and Mannich cyclization of the intermediate iminium-allylsilane, provides piperidine 40b possessing cxo-unsaturation (08BKC1669). 

When Li-Qiang Sun joined the group to initiate his postdoctoral studies, he elected to examine the consequences of adding 57 to the O-methyl analogue of 34 (Scheme 10). While the formation of 58 proved uneventful in the presence of CeCl3, caution had to be exercised while performing the rearrangement/methylation step. We... 

GunstoneM rearranged methyl vernolate (11) to methyl cariolate (12) by treatment... 

Particularly interesting has been the case of Orthosphenia mexicana which yielded five new triterpene methylene quinones with a new carbon skeleton, a greater degree of conjugation than hitherto reported, an extra 14-15 double bond and a rearranged methyl at C-15. Its structure was elucidated by a succession of chemical transformations, spectroscopic methods and X ray diffraction which determined the absolute configuration of this compound [49,50],... 

Methyl l-methyl-2-ethyl-l-cycIopropanecarboxylate heated at 280° until tests indicate near completion of the rearrangement methyl r w5-2-methyl-4-hexe-noate (Y 82.5%) and cw-isomer (Y 17.5%). No rearrangement occurs unless a 2-alkyl group is present in a cw-position. F. e. s. D. E. McGreer and N. W. K. Chiu, Can. J. Chem. 46, 2217 (1968) s. a. W. Ando, Tetrah. Let. 1969, 929. 

Disubstituted ed lenes undogo oxidation with a skeletal rearrangement Methyle yclobutane (17) was oxidized to cyclopentanone via ring expansion (Scheme 3). ... 

Details have been published of Boekelheide s synthesis of [2,2]metacyclophane-1,9-dienes methylation on sulphur of the bis-sulphide (44), Stevens rearrangement, methylation again, and Hoffmann elimination, gave the dimethyl[2,2]metacyclo-phane-1,9-diene (45), which could be isomerized reversibly to trans-15,16-dimethyl-dihydropyrene. [2,2]Metaparacyclophanes and [2,2]metaparacyclophane-l,9-dienes were prepared by similar methods. A second synthesis of [2,2]metaparacyclo-phanes involves preparation and reduction of bis-dithianes, e g. (46), and a third synthesis involved pyrolysis of bis-sulphones obtained by oxidation of disulphides analogous to (44). Ring flipping in substituted [2,2]metaparacyclophanes and... 

Reactions of the alcohols(526)—(528) with acidified methanol have been studied products include those of dehydration, rearrangement, methyl ethers, and ring-cleavage olefins and ethers. ... 

Saunders, M., and P. Vogel Equilibrium Deuterium Isotope Effects in Systems Undergoing Rapid Rearrangements. Methyl Interchange in Dimethylisopropylcarbo-nium Ion. J. Amer. Chem. Soc. 93, 2561 (1971). 

BUTENE. As shown in Figure 38, a group attached to C-1 can migrate from position 1 to 3 (1,3 shift) to produce an isomer. If it is a methyl group, we recover a 1-butene. If it is a hydrogen atom, 2-butene is obtained. A third possible product is the cyclopropane derivative. The photochemical rearrangement of 1-butene was studied extensively both experimentally [88]... 

To obtain a maximum yield of the acid it is necessary to hydrolyse the by-product, iaoamyl iaovalerate this is most economically effected with methyl alcoholic sodium hydroxide. Place a mixture of 20 g. of sodium hydroxide pellets, 25 ml. of water and 225 ml. of methyl alcohol in a 500 ml. round-bottomed flask fitted with a reflux (double surface) condenser, warm until the sodium hydroxide dissolves, add the ester layer and reflux the mixture for a period of 15 minutes. Rearrange the flask for distillation (Fig. II, 13, 3) and distil off the methyl alcohol until the residue becomes pasty. Then add about 200 ml. of water and continue the distfllation until the temperature reaches 98-100°. Pour the residue in the flask, consisting of an aqueous solution of sodium iaovalerate, into a 600 ml. beaker and add sufficient water to dissolve any solid which separates. Add slowly, with stirring, a solution of 15 ml. of concentrated sulphuric acid in 50 ml. of water, and extract the hberated acid with 25 ml. of carbon tetrachloride. Combine this extract with extract (A), dry with a httle anhydrous magnesium or calcium sulphate, and distil off the carbon tetrachloride (Fig. II, 13, 4 150 ml. distiUing or Claisen flask), and then distil the residue. Collect the wovaleric acid 172-176°. The yield is 56 g. 

Davies and Warren" found that when 1,4-dimethylnaphthalene was treated with nitric acid in acetic anhydride, and the mixture was quenched after 34 hr, a pale yellow solid with an ultraviolet spectrum similar to that of a-nitro-naphthalene was produced. However, if the mixture was allowed to stand for 5 days, the product was i-methyl-4 nitromethylnaphthalene, in agreement with earlier findings. Davies and Warren suggested that the intermediate was 1,4-dimethyl-5 nitronaphthalene, which underwent acid catalysed rearrangement to the final product. Robinson pointed out that this is improbable, and suggested an alternative structure (iv) for the intermediate, together with a scheme for its formation from an adduct (ill) (analogous to l above) and its subsequent decomposition to the observed product. 

Two efficient syntheses of strained cyclophanes indicate the synthetic potential of allyl or benzyl sulfide intermediates, in which the combined nucleophilicity and redox activity of the sulfur atom can be used. The dibenzylic sulfides from xylylene dihalides and -dithiols can be methylated with dimethoxycarbenium tetrafiuoroborate (H. Meerwein, 1960 R.F. Borch, 1968, 1969 from trimethyl orthoformate and BFj, 3 4). The sulfonium salts are deprotonated and rearrange to methyl sulfides (Stevens rearrangement). Repeated methylation and Hofmann elimination yields double bonds (R.H. Mitchell, 1974). 

A similar synthesis starts from commercially available 1,5-hexadiyne and 2-methyl-cyclopent-2-enone. The benzocyclobutene is obtained from a bis-acetylene in a cobalt-catalyzed reaction. It rearranges regio- and stereoselectively to a 3-deoxy steroid derivative. The overall yield from the cyclopentenone was 40% (R.L. Funk, 1977). 

Finally a general approach to synthesize A -pyrrolines must be mentioned. This is tl acid-catalyzed (NH4CI or catalytic amounts of HBr) and thermally (150°C) induced tea rangement of cyclopropyl imines. These educts may be obtained from commercial cyan> acetate, cyclopropyl cyanide, or benzyl cyanide derivatives by the routes outlined below. Tl rearrangement is reminiscent of the rearrangement of 1-silyloxy-l-vinylcyclopropancs (p. 7 83) but since it is acid-catalyzed it occurs at much lower temperatures. A -Pyrrolines constitut reactive enamines and may be used in further addition reactions such as the Robinson anei lation with methyl vinyl ketone (R.V. Stevens, 1967, 1968, 1971). 

The (partial) description of the synthesis and coupling of the five fragments starts with the cyclohexyl moiety C —C. The first step involved the enantio- and diastereoselective harpless epoxidation of l,4-pentadien-3-ol described on p. 126f. The epoxide was converted in four steps to a d-vinyl d-lactone which gave a 3-cyclohexenecarboxylate via Ireland-CIaisen rearrangement (cf. p. 87). Uncatalysed hydroboration and oxidation (cf. p. 131) yielded the desired trans-2-methoxycyclohexanol which was protected as a silyl ether. The methyl car-... 

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