Methyl cyclopentanecarboxylates

Methyl cyclopentanecarboxylate has been prepared by the Favorskil rearrangement of 2-chlorocydohcxanonc with sodium... 

Exercise 17-15 When 2-chlorocyclohexanone-2-14C was treated with sodium methoxide, the 14C label in the methyl cyclopentanecarboxylate formed was found at the 1-position (50%) and 2,5-positions (50%) of the ring ... 

Ring-expansion of the 1,3-dione (27a) at —70 °C gives the acetal (28) in low yield, probably via an oxacarbene intermediate.38 The main product, the keto-ester (29) (55%), is formed by the Norrish Type I reaction and is photolabile, forming the ester (30) as well as methyl cyclopentanecarboxylate. The ring-expansion is dependent upon the ring size of the substituent groups and does not occur when the dione (27b) is used. 

JCycloadditions. The anion of the methyl cyclopentanecarboxylate 1 when treated with methyl acrylate undergoes sequential Michael-Michael-Dieckman cyclization to form the spirobicyclic cyclohexanone 8-keto ester 2 as a mixture of two diastereomers (41% yield). Decarboxylation of 2 followed by addition of CHsMgBr... 

The rearrangement can be employed to bring about ring contraction in cycUc systems, for example, 2-chlorocyclohexanone and methoxide ion give methyl cyclopentanecarboxylate in 60% yield (Scheme 3.35). 

Problem 7.13. When 2-chlorocyclohexanone-2- C is treated with sodium methoxide in methanol, labeled methyl cyclopentanecarboxylate results. Careful degradation of the carboxylic acid ester (Chapter 9) showed that the location of the position of the labeled carbon was restricted to three carbon atoms, (a) On which three carbons is the label found (b) What is the distribution of the label (i.e., what percent of the label is found at each carbon) ... 

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