Base-induced rearrangement

An interesting variation of this ring expansion has been described in which the acridane meth-anesulfonate 42 undergoes a base-induced rearrangement accompanied by loss of methanesul-fonate ion to yield 10-phenyl-5//-dibenz[6,/]azepine (43).165... 

Secondly, base-induced rearrangements of porphycenes2-5,6 have been observed to yield isocorroles by ring contraction. Octaethylporphycene 6 when treated with potassium hydroxide in dimethyl sulfoxide/bis(2-methoxyethyl) ether (diglyme) was found to give a mixture of octa-ethylisocorrolecarbaldehydc 7 and octaethylisocorrole 8. The ratio of the compounds varies depending on the reaction conditions. 

Base-induced rearrangement of bicyclo[2.2.2]octane oxide 67 gives predominantly bicyclo[2.2.2]octanone 68 (Scheme 5.15), which once again indicates that close proximity between the carbenoid center and the C-H bond into which it may insert is important if such an insertion is to occur [30]. In comparison, the sense of product distribution is reversed for the related substrate bicyclo[2.2.2]octadiene oxide 70 on treatment with LDA [15, 22], alcohol 72 being the favored product. 

Lubineau A, Aug6 J (1999) Water as Solvent in Organic Synthesis. 206 1-39 Lundt I, Madsen R (2001) Synthetically Useful Base Induced Rearrangements of Aldonolac-tones. 215 177-191... 

Biosynthesis of the spirobenzylisoquinoline alkaloid ochotensimine (282) via the quinomethide intermediate (Scheme 49) was proposed by Shamma and Jones (7J0). On the basis of this hypothesis, several biomimetic transformations of phenolic protoberberines to spirobenzylisoquinolines have been realized by the base-induced rearrangement via the quinomethide. 

Scheme SO. Synthesis of the ochotensimine analog 288 from a phenolic protoberberine by base-induced rearrangement. Reagents a, LAH b, Mel c, HBr d, NaOH, aq EtOH e, DMSO.

Finally, there are base-induced rearrangements involving carban-ions that proceed via 1,3-elimination to form cyclopropanone inter-... 

Tetrahydropyran epoxides 12, the synthesis of which involves a RCM, undergo a base-induced rearrangement to 3,4-dihydro-2//-pyran-4-ols 13. These compounds are converted stereospecifically to 3,6-dihydropyrans 14 on treatment with allyltrimethylsilane (Scheme 6) <00EJO3145>. 

BASE-INDUCED REARRANGEMENT OF EPOXIDES TO ALLYLIC ALCOHOLS trans-Pinocarveol,... 

A similar base-induced rearrangement has been reported to occur at room temperature with the Z-isomer of 3-methyl-4-benzoylfuroxan oxime (143), yielding the 3-(a-nitroethyl)-4-phenylfurazan (144) (82G181), and with 3,4-diformaldoxime furoxan (145), which gives 3-(a-nitroacetal-doxime)furazan (146) (Scheme IV.57) (81AHC(2G)251). 

Examples of the Dimroth rearrangement (Section IV, F) include several s3mtheses of monocyclic triazoles from other heterocyclic systems (cf. Scheme 25). Triazole-5-thiols can be prepared by treatment of 5-amino-l,2,3-thiadiazoles with bases.A similar base-induced rearrangement of sydnoneimines provides a synthesis of 4-hydroxy-triazoles. ... 

Harger has studied the rearrangement of A-substituted N-phosphinoylhydroxylamines in the presence of base . He proposed a concerted mechanism based on the observed retention of the configuration at the phosphorous center during the transposition , and on studies with 0-labelled compounds . Similar cyclic transition states 572 were proposed in the base-induced rearrangement of A,0-bis(diphenylphosphinoyl)hydroxylamines (571) (equation 254). However, in the rearrangement of O-benzoyl-A-(diphenylphosphino-thiol)hydroxylamine where a transposition of O and S atoms occurs, the proposed cyclic transition state has sulfur participation . 

Our opinion is that the actual configuration of oximes 37 should be inverted. Nitrosation of 36 in the presence of an alcoholate should result in the two E and Z oximes the Z isomer will suffer a spontaneous base-induced rearrangement into the furazan 39 and will not be isolated. Furthermore, the reported spectroscopic data agree with the inverted configuration. The intermediacy of open-chain species in the rearrangement... 

From the 3-acetyloxadiazole 54 (R = Me), both E and Z phenylhydra-zones55(R = Me R = H) are obtained, the isomer being the predominant component. As expected, both isomers rearrange on melting into the triazole 57 (R = Me), whereas the base-induced rearrangement takes place preferably from the Z isomer only (90UP1). 

Some A -l,2,4-oxadiazolyl-A -arylureas (115) have been synthesized, and their base-induced rearrangement into the benzoylamino-l,2,4-tria-... 

Base-induced rearrangement of quaternized thiazoles results in the formation of formamido-methylene thietanes (128) (Eq. 18). 

A base-induced rearrangement initiated by cyanide is possible with 2-bromobicyclo[3.2.0]heptan-6-ones. The rearrangement proceeds via a cyclopropane.243,244... 

Similar base-induced rearrangement of 4-(l-bromopentacyclo[4.3.0.02-5.03-8.04,7]nonan-9-onyl ethylene acetal)methyl phenyl sulfone (68) leads also to an almost quantitative yield of l-bromo-4-(benzenesulfonylmethyl)tricyclo[4.2.1.02-5]nona-3,7-dien-9-one ethylene acetal (69), together with a trace amount of l-bromo-4-(benzenesulfonylmethylidene)tricyclo[4.2.1.02,5]-non-7-en-9-one ethylene acetal (70).171... 

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