Nickel cyclobutanones

A nickel(O) complex catalyzes insertion of alkynes into cyclobutanones (Equation (79)).437 Formation of metalla-cycle 194 via oxidative cyclization of an alkyne with the carbonyl group of a cyclobutanone followed by /3-carbon elimination (formation of metallacycle 195) and reductive elimination are postulated for the mechanism (Scheme 92). 

A common alternative to the Wolff-Kishner reduction of cyclobutanones to the parent cyclobutane (see Section S.2.4.2.), is formation of thiocetals (see Section 5.2.4.7.1.) followed by hydrogenolyses using Raney nickel.64,146-149 For example, l,4,4-trimethyl-6,6-(propane-l,3-diyldithia)bicyclo[3.2.0]heptan-3-one gave 15 using this method. It was found that the W-2 quality of Raney nickel works well.64"148... 

Cyclobutanone equivalent.1 U se of lithium 1 -dimethylaminonaphthalenide (10, 244) or Raney nickel for desulfuration permits use of 1 as a surrogate for cyclobutanone, which can not be monoalkylated satisfactorily. Some synthetic uses are formulated in equations (II) and (III). 

A nickel-catalysed alkyne insertion between the carbonyl carbon and the -carbon of the cyclobutanone was achieved by combining a ketone-alkyne coupling reaction with a /3-carbon elimination process (Scheme 79).121 The reaction uses cyclobutanones as a four-carbon unit and provides access to substituted cyclohexenones. 

In 2012, Murakami et al reported the asymmetric intramolecular alkene insertion reaction of 3-(2-styryl)cyclobutanones catalysed by an in situ generated chiral nickel complex bearing a BINOL-derived phosphoramidite ligand 15 (Scheme 10.22). The reaction provided a unique and straightforward access to... 

Scheme 6 Nickel-catalyzed intramolecular insertions of olefins into a cyclobutanone C-C bond...

Ashida S, Murakami M (2008) Nickel-catalyzed 4+2+2 -type annulation reaction of cyclobutanones with diynes and enynes. Bull Chem Soc Jpn 81(7) 885-893. doi 10.1246/ bcsj.81.885... 

Murakami M, Ashida S, Matsuda T (2005) Nickel-catalyzed intomolecular alkyme ins on into cyclobutanones. J Am Chem Soc 127(19) 6932-6933. doi 10.1021/ja050674f... 

Murakami M, Ashida S (2006) Nickel-catalysed intramolecular alkene insertion into cyclobutanones. Chem Conunun 44 4599-4601. doi 10.1039/b611522e... 

Transition metal alkoxides of tert-cyclobutanols undergo ring opening by P-carbon elimination to generate ketones that are metalated at the y-position these can be utilized in many functionalization reactions. Palladium, rhodium, and nickel have been the most studied metals in these transformations. Useful transition metal cyclobutanolates are generated from either cyclobutanones or cyclobutanols. 

Cyclobutanone 58 reacted with alkyne in the presence of nickel(O) catalysts to produce cyclohexenone 59 via a [4-1-2]-type annulation (Scheme 3.32) [41]. Oxidative cyclization of the carbonyl group of cyclobutanone and the alkyne with nickel(O) was followed by p-carbon elimination from the resulting oxanickelacy-clopentene and subsequent reductive elimination. 

Intramolecular insertions of alkenes into cyclobutanones were catalyzed by a nickel(O) complex (Scheme 3.34) [44]. 3-(2-Alkenylphenyl)cyclobutanones were converted into ketones having a bicyclo[2.2.2] octane skeleton. 

Murakami et al. reported a nickel-catalyzed alkyne/alkene insertion reaction into a C(carbonyl)-C(sp ) bond of cyclobutanones [21] and applied it to the enantioselective synthesis of benzobicyclo[2.2.2]octenones (Scheme 8.4) [22]. [2-f2] Cycloaddition of 1,2-divinylbenzene 24 with dichloroketene followed by... 

The nickel-catalyzed intermolecular reaction [4+2+2]-annulation of diynes with cyclobutanone as C4 fragment includes the ring expansion... 

Scheme 2.90 Postulated mechanism for the nickel-catalyzed intermolecular [4-I-2-I-2] annulation reaction of cyclobutanones 2.269 with diynes 2.268.

---