Ketones, cyclopropyl ring opening

Cyclopropyl groups have been used to probe for ketyl anion intermediacy in reactions of Sml2 with ketones. In 1991, Molander reported that treatment of cyclopropyl ketone 15 with Sml2 yields ring-opened product 16 in 81% overall yield (equation 10)56 Timberlake and Chen reported that several cyclopropyl-ring-opened products result from treatment of 17 with Sml2 (Scheme 17)57. 

Cyclopropyl ketones (19, R1 = Me, Et, cyclopentyl) have been converted to enamines (20 R2N = Me2N, Et2N, pyrrolidino, morpholino), but when R = aryl or cyclopropyl, ring opening occurs153. 

Cleavage of Cyclopropyl Ketones.Cyclopropyl ketones undergo ring opening with TMS-I, via the silyl enol ether (eq 16). Cyclobutanones react analogously under these conditions. 

A different example involving cyclopropyl ring-opening is provided by a benzoylcyclopropane which cyclizes normally and ring-opens as a type II cleavage to generate a 5,6-unsaturated ketone. ... 

Reductive opening of the cyclopropyl ring in 9j5,19-cycloandrostan-ll-one (234) has been achieved by treatment with a large excess of sodium in iso-propanol-OD. Analysis of the product for isotopic purity after oxidation to the corresponding ketone and base-catalyzed back exchange of the 9a-deuterium [(235) (236)] shows 19% do and 10% 62 isotopic impurities. The 10% 62 product is probably due to incomplete back exchange. 

Treatment of oc-cyclopropyl ketones with lithium in a mixture of N,N-d2 propylamine and hexamethylphosphortriamide is a recently reported method for deuterium labeling via reductive ring opening. This reaction provides y-labeled ketones in good yield (70-100%) and isotopic purity (85-93%). 

Ring opening due to intramolecular hydrogen abstraction has been demonstrated for cyclopropyl ketone derivatives 1035 ... 

Another interesting cationic domino process is the acid-induced ring opening of a-cyclopropyl ketones and subsequent endocyclic trapping of the formed carboca-... 

Scheme 3.44. General scheme of domino radical ring-opening reactions of cyclopropyl ketones...

MoC15 promotes the ring-opening transformations of cyclopropyl ketones. Cyclopropyl phenyl ketone 251 is converted to 1-phenyl-1,2,4-trichloro-1-butene 252. Desilylative lactonization of propyl 2-(trimethylsilylmethyl)cyclo-propanecarboxylate 253 yields ds-2-chloro-4-pentanolide 254 stereoselectively [144]. (Scheme 100)... 

Cycloadduct 212 is converted into the dihydrobenzofuran 213 when treated with boron trifluoride diethyl etherate in good yield <2000JA8155>. The formation of the dihydrobenzofuran proceeds by an initial ring opening followed by a subsequent dehydration and acid-catalyzed cyclopropyl ketone rearrangement (Equation 142). 

Section 1.1.1.3.1.1.2.1.). Similarly, the reductive ring opening of cyclopropyl ketones, e.g., 8, with lithium in ammonia affords specific enolates20,21. These enolates can, of course, be used for selective alkylation. Furthermore, enol acetates, e.g., 10, are regiospecifically obtained by nucleophilic ring opening of cyclopropyl ketones21. 

The method is a modification of one used by Barton and McCombie.8 Reduction of ketones.9 Ketones can be reduced to alcohols by Bu3SnH in the presence of either AIBN or a Lewis acid, but this reaction is limited to unhindered ketones. However, even sterically hindered ketones, such as f-butyl methyl ketone, can be reduced under high pressure (10 kbar) in the absence of a catalyst. This method is particularly useful in the case of cyclopropyl and a,p-epoxy ketones, which are reduced to the corresponding alcohols. Reduction of these ketones with Bu3SnH under radical conditions results in ring-opened products. 

In 1990, Tanko and Drumright51 presented evidence that the ring opening of the radical anion generated from phenyl cyclopropyl ketone (Scheme 15) is reversible, with an... 

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