Rearrangements iodotrimethylsilane

Likewise, synthetic 2//-azepines isomerize to 3//-azepines in refluxing chloroform (2-3 h) or in tert-butyl methyl ether at room temperature.291 The isomers can be readily separated by chromatography on silica gel, as the more basic 2//-azepines30 have lower Rf values. In contrast, 7-butyl-2//-azepin-2-acetic acid (11), obtained by heating the tert-butyl ester 10 with iodotrimethylsilane, is stabilized by intramolecular hydrogen bonding and shows no tendency to rearrange to the 3//-isomer.291... 

Rearrangement of the tricyclo[5.4.0.02,6]undecane-8,ll-dione with iodotrimethylsilane gave tricyclo[6.3.0.02,6]undcc-2(6)-en-3-one 2,17 while the tetrakisspirocyclobutane system 3 gave 4 on rearrangement with /Moluenesulfonic acid.18... 

In the presence of proton and/or Lewis acid and strong nucleophiles bicyclo[3.2.0]heptan-6-ones are converted to 3-substituted cycloheptanones (Table 15). Bicyclo[3.2.0]heptan-6-ones rearrange to give 3-iodocycloheptanones on treatment with iodotrimethylsilane. Zinc(II) iodide or mercury(II) halides as catalysts enhance the rate and the selectivity of the reaction.31 If a second, enolizable carbonyl group is present, an intramolecular alkylation may follow the ring enlargement under these reaction conditions.32 Consecutive treatment with tributyltin hydride/ 2,2 -azobisisobutyronitrile affords reduced, iodo-free cycloheptanones, whilst treatment with l,8-diazabicyclo[5.4.0]undecene yields cycloheptenones.33 Similarly, benzenethiol adds to the central bond of bicyclo[3.2.0]heptan-6-ones in the presence of zinc(II) chloride and hydrochloric acid under anhydrous conditions to form 3-(phenylsulfanyl)cycloheptanones.34... 

Little quantities of iodotrimethylsilane catalyse the rearrangement of 2-siloxy cyclopropanes to their isomeric silyl enol ethers (equation 102), whereas an equimolar amount of this silylating agent gives a highly donor substituted diene. Both product types are promising intermediates, yet their chemistry still remains to be explored. 

Some of the low-temperature rearrangements listed in this section take place under Lewis acid catalysis (iron(III) chloride, iodotrimethylsilane, zinc(II) bromide, 010.]. °... 

This methodology can also be applied to the synthesis of heterocycles. Thus, the rearrangement of 4 a or 4b, derived from (S )-alanine or (S )-valine using the premixed method (see p 3468)615, gives 5 a or 5 b as single diastereomers which, after deprotection with iodotrimethylsilane in chloroform, afford pyrrolidine derivatives 6329. 

A neat four-step synthesis of the triquinane sesquiterpene hirsutene (4) has been described, which features the novel iodotrimethylsilane induced rearrangement of the dione (1), to (2), as a key step. Reductive methylation of the enone (2) to (3),followed by Wittig methylenation then completed the synthesis. ... 

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