Isomerization with methyl magnesium

Cydopentene oxide and 1 -methylcyclopentene oxide yield respectively Iran - 2 -methyloyclopentanol and a mixture of cie- and Iran 1.2-dixnethylcyclopentanol (Eq. 851) on treatment with methyl-magnesium iodide. 0 - . The latter could in principle be formed either by a preliminary isomerization to 2-methyJcyolopentanone, or by direct addition to the least-substituted epoxide carbon atom. These possibilities have not, however, been distinguished until now. 

When the ethylene oxide contains an aromatic substituent, as in styrene oxide, there is a significant tendency for preliminary isomerization to oocur. Thus, treatment of styrene oxide with methyl-magnesium bromide or ethylmagnesium bromide yields 1 -phenyl-2-propauol and l-phemyJ-2-butanol respectively1 83 (Eq. 841). 

Reactions of the corresponding ketones have been much less studied, but alkylation reactions appear to be highly antiselective relative to the metal. Some alkylations resulting in the isomerization of the diene geometry have been observed. For example, reaction of (85) with methyl magnesium bromide gives (86) but reaction with methyl lithium affords (87) (Scheme 137). Related reductions of dienone iron complexes with sodium borohydride are also highly antiselective. 

Conjugate addition of methyl magnesium iodide in the presence of cuprous chloride to the enone (91) leads to the la-methyl product mesterolone (92) Although this is the thermodynamically unfavored axially disposed product, no possibility for isomerization exists in this case, since the ketone is once removed from this center. In an interesting synthesis of an oxa steroid, the enone (91) is first oxidized with lead tetraacetate the carbon at the 2 position is lost, affording the acid aldehyde. Reduction of this intermediate, also shown in the lactol form, with sodium borohydride affords the steroid lactone oxandrolone... 

Benzyltrimethylsilicane occurs from the interaction of benzyl-trichlorosilicane and methyl magnesium bromide. It boils at 191 2° to 191 4° C., is isomeric with phenyldimethylethylsilicane and is a colourless liquid, having a strong odour resembling anisole. ... 

Other rearrangements in this class include the allylacetylene-vinylallene isomerization with various substituent groups the reaction of methyl-magnesium iodide and magnesium iodide with propargyl acetates the... 

In the context of a chemical study related to problems of vitamin B12 biosynthesis, peripheral C-methylation of the magnesium complex of tctct-OEPc (17) was reported to yield a mixture of isomeric products (18a-c) (83AG(E)631). A similar reaction was found to occur at C-12 of nonamethyl pyrrocorphin (19). One of the by-products of this reaction is the seco-corphinoid derivative 20, which, on complexation with Ni(II) acetate, cyclizes to give an Ni(II) corrinate (21) (84CC583). 

Reaction of methyl quinolinylsulfoxide (86) with allylmagnesium chloride or with 1-methylallyl-magnesium chloride led to the 2-allyl and 2-(l-methylallyl)quinoline, (87) and (88) respectively, contaminated with unseparable isomeric a,p-unsaturated derivatives, in high yields. ... 

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