Methyl hydrogen 3-methylglutarate

Pure j3-methylglutaric anhydride melts at 46°.6 The jS-methylglutaric anhydride obtained in this preparation varies in its appearance at 25° from an almost completely crystalline mass to a mixture of about one-third solid and two-thirds liquid. However, the submitter has found that product of either appearance can be converted to methyl hydrogen /3-methylglutarate in 80-85% yield. Further purification is troublesome, and the product of the present procedure is pure enough for most purposes. 

Methyl hydrogen 3-methylglutarate, A32.5, A"39 Methyl 3,4-dideoxyglucose, Y"14.11 Spirobi-1,4-dioxan, X"2.10 C7H12O4S... 

Methylformanilide, 23, 43 Methyl-/3-formylpropionate, 21, 88 a-Methylglucoside, 20, 99 /3-Methylglutaric acid, 23, 60 Methyl hydrogen adipate, 26, 52 Methyl hydrogen succinate, 25,19 4-Methyl-7-hydroxy-8-acetylcouma-... 

Optically active phytol has been synthesised (ref. 75) and the methodology is depicted in Scheme 24. In this route (R)-(+)-citronellol was converted to 4(R),8-dimethylnonanoic acid which was then anodically cross-coupled with methyl hydrogen 3(R)-methylglutarate to give 3(R), 7(R), 11-trimethyldodecanoic acid. Similar cross-coupling with levulinic acid afforded 6(R),10(R),14-trimethylpentadecan-2-one and reaction with methoxyacetylene followed by acidic treatment gave a mixture of cis and trans methyl phytenoates which were separated. Reduction of the trans ester with lithium aluminium hydride resulted in phytol identical with the natural product. 

Dimerization of methyl crotonate has been carried out with alkaline earth metal oxides as basic catalysts 15). The reaction proceeds by Michael addition, which is initiated by abstraction of an allylic hydrogen of methyl crotonate by the basic site to form the allylic carbanion, which attacks a second methyl crotonate molecule at the jS-position to form a methyl diester of 3-methyl-2-vinylglutaric acid. The diester undergoes a double bond migration to form the final E- and Z- isomers of 3-ethylidene-3-methylglutaric acid dimethyl ester (MEG) (Scheme 22). 

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