Myers rearrangement

In addition to the sulfur-substituted enyne-allenes depicted in Schemes 20.18-20.20, the sulfoxide 141 was prepared by treatment of the enediynyl propargylic alcohol 108 with benzenesulfenyl chloride to induce a [2,3]-sigmatropic rearrangement (Scheme 20.29) [10]. The Myers-Saito cyclization of 141 occurs at 37 °C with a half-life of only 16 min. 

When 160 was heated at 150 °C in the presence of 1,4-CHD, the naphthalene derivative 163 was obtained in 45% yield (Scheme 20.32) [56, 67]. An initial [3,3]-sigmatro-pic rearrangement to form 161 followed by a Myers-Saito cyclization and hydrogen-atom abstractions from 1,4-CHD could account for the formation of 163. 

The use of the zinc-copper couple to effect the reduction of the methanesulfonate 168 with rearrangement furnished 169 (Scheme 20.34) [10]. Treatment of 168 with methylmagnesium bromide in the presence of copper(I) cyanide to induce an SN2 -type reaction produced the methylated adduct 170. The half-life of the Myers-Saito cyclization of 169 is 66 h at 37 °C, whereas that of 170 is 100 min. The faster rate of cyclization for 170 has been attributed to a steric effect favoring the requisite s-cis or twisted s-cis conformation. 

In addition to the example depicted in Scheme 20.40 and examples involving a prototropic rearrangement [61], the use of trimethylsilyl trifluoromethanesulfonate to induce the transformation of 212 afforded 213 bearing a keto substituent at the allenic terminus (Scheme 20.44) [81]. Thermolysis of 213 promoted the Myers-Saito cyclization leading to 216. 

Figure 14.5 Schematics for the Barr-ll and Barr-Ill barrier screw technologies a) full-length schematic of a Barr-ll barrier screw, b) expanded view of the barrier entry section of a Barr-ll screw, c) full-length schematic of a Barr-Ill barrier screw, d) expanded view of the barrier entry section of a Barr-Ill screw, and e) expanded view of the crossoverflow rearrangement section at the exit of Barr barrier screws (Schematics courtesy of Jeff Myers of Robert Barr, Inc.)...

The prototype of this reaction is the Myers-Saito reaction, the rearrangement of eneyneallene (Z)-hepta-l,2,4-triene-6-yne (70) to a,3-didehydrotoluene (71). This C2—C7 cyclization yields a benzylic 7i-conjugated a,7t-biradical and is therefore... 

Myers, A. G. Siegel, D. R. Buzard, D. J. Charest, M. G. Synthesis of a broad array of highly functionalized, enantiomerically pure cyclohexanecarboxylic acid derivatives by microbial dihydroxylation of benzoic acid and subsequent oxidative and rearrangement reactions. Org. Lett. 2001, 3, 2923-2926. 

The study of Bergman, Myers-Saito and related biradical cyclizations using an unrestricted broken spin symmetry approach refined by single-point energy coupled-cluster calculations has been reviewed, and a simple rule outlined for predicting biradical involvement in such Cope-type rearrangements radicals were found to be probable... 

Quantum chemical studies of cyclizations of enediynes and enyneallenes have been reviewed.180 The intermediates are computationally tractable as a result of the unrestricted broken spin symmetry (UBS) approach using GGA functionals for the description of open-shell biradicals. The intermediacy of biradicals in Cope-type rearrangements, to which the Bergman and Myers-Saito reactions belong, are shown to be predictable using a very simple rule biradicals are likely to be intermediates if they are stabilized either by allyl resonance or by aromaticity. 

As part of an effort to find methods for the deprenylation of lipopeptides, Bristol-Myers Squibb chemists successfully applied the ME rearrangement toward this end (Scheme 46) [115]. After oxidation ofthe model compound 170 the resulting diastereoisomeric sulfoxides (not shown) were heated in benzene in the presence of various thiophiles. If triphenylphosphane was used for... 

Several vinylcyclopropane to cyclopentene rearrangements have been reported in which a cationic substituent appears to facilitate the reaction. For example, exposure of (150 equation 23) to excess di-ethylaluminum chloride at 0 C for 12 min furnished (151), which served as a key intermediate in Corey and Myers synthesis of the plant hormone antheridogen-An. Attempts to effect this transformation thermally were unsuccessful. In a similar fashion, treatment of (152 equation 24) with boron tribromide induced VCP rearrangement of this compound at room temperature, probably via initial cleavage to the allylic carbocation (153). The reaction of the analogous vinylcyclopropane lacking a phenyl group failed to go to completion under these conditions. 

Boyer, J. L., Krum, J. E., Myers, M. C., Fazal, A. N., Wigal, C. T. Synthetic Utility and Mechanistic Implications of the Fries Rearrangement of Hydroquinone Diesters in Boron Trifluoride Complexes. J. Org. Chem. 2000, 65,4712-4714. 

In contrast to di-radicals such as 121 (Scheme 19.33), di-radicals originated by the Myers-Saito rearrangement are known to have an ionic character in protic solvents and this nature is thought to reduce their DNA damaging ability. However, it has been shown by Shibuya that the presence of an electron withdrawing group in the benzylic position produces a dehydrotoluene species with an enhanced diradical character. 

Recently, Myers cyclizations were used to synthesize naphthalenic and benz[e]indene systems. Grissom and co-workers have constructed them from ene-diyne vinyl ether precursor 128 [46], The major pathway involves a Claisen rearrangement of 128 to provide the enyne-allene intermediate 129, which quickly undergoes Myers cycliza-tion to provide aldehyde 131 (Scheme 23). Bergman cyclization of the ene-diyne system to yield the tricyclic ether, 134, constitutes the minor pathway. 

Silver(I)-catalyzed [3,3]-Sigmatropic rearrangement and Myers-Saito cyclization of l-(2-Ethynylphenyl)hept-2-yn-l-yl pivalate (69) l-(2-Naphthyl)pentan-l-one (71) ... 

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