Tris methyl derivatives rearrangement

N-methyl 78 and 7-methoxy derivatives 79, whereas dimethyl sulfate and tri-methyloxonium tetrafluoroborate gave only the 7-methoxy derivative 79 (92CB929). Although the 11-methoxy derivative 77 could be rearranged to the A-methyl derivative 43 by heating in a mixture of toluene and DMF for 17 h in the presence of a small amount of pyrido[l,2-h]cinnolinium-ll-olate (17, R = H), no isomerization to the A-methyl derivative 78 occurred when the 7-methoxy compound 79 was heated in the presence of pyrido[2,l-a] phthalazinium-7-olate (20) (92CB929). 

Korhonen has also studied the El-induced fragmentation of a series of chlorinated methyl propenoates, comprising cis and trans isomers of all the mono-, di- and tri-chloro derivatives, and their trideuteromethyl derivatives211. One aspect which was examined in detail concerns the effect of the position of chlorine substituents on the isomerization of the substrate molecular ion, as depicted in Scheme 29 for 2-chloropropenoate. This isomerization, which had already been observed212, is revealed by the formation of [M - H20]+ and [M - C02H]+ ions typical of acids. This rearrangement is particularly favored for 2-chloropropenoate, but also takes place, although to a lesser extent, for cis-3-chloro- and... 

Methylenation of tri-O-benzyl-D-arabinolactone 335 (Scheme 115) with BT methyl sulfone gave [148] the expected adduct (not shown in the scheme) under the standard conditions in 78% yield. However, the rearrangement step was retarded. Methylene exoglycal 337 was eventually obtained in 66% yield when the reagents were treated first with LHMDS in THF at - 78 °C and then with DBU at rt. The method was applied to various sugar lactones with pyra-nose or furanose rings to give the respective methylene derivatives in 46- 74% yields. 

Bayer and Siebert tried to exchange methyl for iodine in 2-(2,2-dimethyl-propylidene)-4,5-diethyl-l,3-diiodo-2,3-dihydro-17/-l,3-diborole 22 by reacting with trimethylaluminium in pentane at -15°C <2002ZN1125>. However, due to the instability of the 1,3-dimethyl derivative 40, it was detected only by H NMR spectroscopy before rearranging into nido-Gt carboranes 41 and 42, as well as to polymeric materials (Scheme 2). 

Eaborn for several years has been studying the properties of tris(trimethylsilyl)methyl (trisyl) compounds, particularly their silyl derivatives. 1,3-rearrangements of alkyl groups between silicon atoms has been observed, and bridged cations have been proposed as intermediates. It has recently been observed that several reactions of the iododiphenylsilyl derivative were influenced by ultraviolet irradiation. Depending on the... 

Schreiber et al. have been able to apply their enediyne intramolecular Diels-Alder approach to the synthesis of dynemicin model systems [268-270], culminating in the total synthesis of di- and tri-O-methyl dynemicin A methyl esters 388 and 389 (Scheme 7-78) [271], derivatives of the natural product itself. Highlights of this synthetic approach include (a) intramolecular lactonization and concomitant Diels-Alder cyclization (380- 381) (b) allylic hydroxylation followed by an allylic diazene rearrangement in order to regiospecifically isomerize a double bond (381 - 382) (c) a-hydroxylation of the lactone 381 and subsequent conversion to the P-ketoester 383 (d) annelation of the anthraquinone unit (383- 384- 385- 386) (e) mild base-induced P-elimination of the N-protecting group of 386 to give the free amine 387 and (f) a final oxidation to complete the anthraquinone (387 - 388). 

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