Methyl-4-methylpent-3-enoate

In contrast to Mori s synthesis, Pawar and Chattapadhyay used enzymatically controlled enantiomeric separation as the final step [300]. Butanone H was converted into 3-methylpent-l-en-3-ol I. Reaction with trimethyl orthoacetate and subsequent Claisen-orthoester rearrangement yielded ethyl (E)-5-methyl-hept-4-enoate K. Transformation of K into the aldehyde L, followed by reaction with ethylmagnesium bromide furnished racemic ( )-7-methylnon-6-ene-3-ol M. Its enzyme-catalysed enantioselective transesterification using vinylacetate and lipase from Penicillium or Pseudomonas directly afforded 157, while its enantiomer was obtained from the separated alcohol by standard acetylation. 

Other examples showing relevant intramolecular nucleophilic substitution are the cyclization of ethyl 3-(2-chloroethyl)-3-methylpent-4-enoate to give ethyl 2-methyl-2-vinylcyclobutane carboxy-late (22).21... 

A. Methyl Z-2-(bromomethyl)-4-methylpent-2-enoate.2 A dry, 250-mL, threenecked, round-bottomed flask fitted with an overhead stirrer and nitrogen inlet is charged with 100 mL of dichloromethane (CH2CI2, Note 1) and 25.9 g (0.15 moi) of N-bromosuccinimide (Note 2). The stirred suspension is cooled to 0°C and 9.29 g (0.15 mol) of dimethyl sulfide (Note 3) is added (Note 4), followed by 15.8 g (0.10 mol) of methyl 3-hydroxy-4-methyl-2-methylenepentanoate (Note 5). The resulting mixture is allowed to warm to room temperature, stirred for 24 hr, recooled to 0°C, diluted with 150 mL of pentane (Note 6), and poured into 200 mL of saturated brine and ice. The... 

Methyl Z-2-(bromomethyl)-4-methylpent-2-enoate 2-Pentenoic acid,... 

Dichloro-3.3,3-trifluoropropanal, an intermediate for the production of substituted pyridines, was prepared by ozonolysis of methyl 4,4-dichloro-5,5.5-trifluoro-2-methylpent-2-enoate with reductive workup. ... 

Reaction of methyl 4-bromo-2-methoxycarbonyl-4-methylpent-2-enoate (24) with 3.2 equivalents of sodium cyanide in dimethyl sulfoxide at 20 °C for 3 hours leads to the formation of dimethyl 3-cyano-2,2-dimethylcyclopropane-l,l-dicarboxylate (25) which is readily de-methoxycarbonylated to give tra 5-3-cyano-2,2-dimethylcyclopropanecarboxylic acid (26) in 67% overall yield. This compound can be conveniently transformed into chrysanthemic acid and hemicaronic aldehyde. ... 

The previously mentioned carbonyl variant of the 1 - 3 hydrogen migration process is most clearly illustrated by the behavior of the epimeric methyl 2-methylcyclopropanecarboxylates (80). Whereas the cw-isomer 80 rearranges to methylpent-4-enoate (82) on heating to ca. 250 °C with AH = 35.9 kcal mol and dS = —17 e.u., the trans-isomer tranj-80 was reported to be stable under the same conditions. ... 

Draw (a) 5-phenylhex-3.B-en-2-one, (b) methyl 2,2-diethylhept-4.B-enoate, and (c) 4-methylpent-2-ynal. 

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