Trimethylsilyl group, ring expansion

The kinetic data for these reactions are numerous, as shown in Table VI. Most of values were obtained by radical clock methods. The ring expansion of radical 7 has been employed as the clock in a study that provided much of the data in Table VI.74 Cyclizations of 5-hexenyl-type radicals also have been used as clocks,75-77 and other competition reactions have been used.78 Hydrogen atom abstraction from n-Bu3GeH by primary alkyl radicals containing a trimethylsilyl group in the a-, >8-, or y-position were obtained by the indirect method in competition with alkyl radical recombi-... 

There is a paucity of functional group reactions associated with the pyrrolopyrazines. A few examples may be found within the references describing their syntheses. However, a reaction has been reported which describes the [4 + 2] cycloaddition of pyrrolopyrazines. Ring expansion of 2-phenyl-2//-pyrrolo[3,4-/ ]pyrazine (32) occurs through cyclocondensation of the trimethylsilyl ether (33) with, amongst other dienophiles, methyl acrylate, and a mixture of quinoxalines (34) is obtained in 38% yield (Scheme 2) <86JHC1641>. 

A ring expansion by two carbon atoms was discovered on heating (Z)-l-vinyl-cyclonon-3-en-l-yl-trimethylsilyl ether (V/62), Scheme V/10 [31] [32], Two types of trimethylsiloxy enol ethers were observed, each formed by a [1.3] or a [3.3] sigmatropic shift which, after hydrolysis, gave the ketones V/63, V/64, and V/65. The protection of the tertiary alcohol function is not necessary, if the reaction is done in the presence of potassium hydride [33] [34]. The reaction proceeds when the cyclic 1-vinyl alcohols have either a double bond or a benzo group at the 3-position. Other examples of this reaction type are given in Scheme V/10. 

Another variation of this ring expansion used sulfur stabilized cations. When aldehyde 65 was treated with trimethylsilyl methyl sulfide and trimethylsilyl triflate, cation 66 was formed and rearranged to the more stable tertiary cation 67. Elimination of the silyl group gave a 59% yield of the ejco-methylene derivative (68). 9... 

A chiral l-isopropenyl-l-(3-oxopropyl)disilane derivative undergoes a type n ene cycloaddition under Lewis acid conditions via a 1,2-migration of a trimethylsilyl group. The ring expansion of 7-boranorbornadienes by coordination with an NHC... 

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