Vinylcyclopropyl ketones

IS-Addition to a vinylcyclopropyl ketone22 Concluding steps in a recent synthesis of ( + )-modhephene (3) required the introduction of a methyl group by a novel 1,5-addition of (CH3)2CuLi to the vinylcyclopropyl ketone (1) to afford 2 after in situ enolate trapping with N,N-dimethylphosphoramidic dichloride.24 The synthesis of 3 was completed by reduction of the phosphordiamidate group and hydrogenation. 

Cycloheptane annelation (7, 212). The mixed cuprate 1 reacts with acid chlorides to afford vinylcyclopropyl ketones. Previously these ketones were prepared from aldehydes by condensation with l-lithio-2-vinylcyclopropane followed by oxidation (7, 192-193). These compounds are rearranged to 4-cycloheptenones on conversion to trimethylsilyl enol ethers, thermolysis, and hydrolysis. ... 

Using a somewhat similar reaction sequence cw-l-bromo-2-vinylcyclopropane was reacted with various acid chlorides and transformed stereospecifically to 1-acyl-2-vinylcyclopro-panes. Very good yields were obtained thus, when the bromide was allowed to react successively with tert-butyllithium, phenylsulfanylcopper and cyclobutanecarbonyl chloride at — 78 °C, cyclobutyl d5-2-vinylcyclopropyl ketone (2a) was isolated in 93% yield. 

Trialkylboranes react with alkyl 2-vinylcyclopropyl ketones, e.g. 63, in the presence of oxygen, to afford substituted alkyl pent-3-enyl ketones in low yields. 

Vinylcyclopropanation of Enones. Conjugate addition of sulfur-stabilized aUyl carbanions to a. -unsaturated ketones produces enolates that cyclize to vinylcyclopropyl ketones upon treatment with nearly one equivalent of (CuOTf)2-C6H6, i.e. 1.9 equivalents of Cu (eq 68). ... 

Ring closures of hydroxyketones Vinylcyclopropyl ketones from y,d-ethylene- -liydroxyketones by stereospecific cyclodehydration... 

Alkylidenecydopropane derivatives can readily be prepared by the reaction of 1 with vinylcyclopropyl carbonates and subsequent trapping of the resulting allyltitaniums with aldehydes or ketones (Eq. 9.24) [44], It should be noted that, in this case, the carbon—carbon bond formation occurs at the less substituted allylic terminus, and not at the more substituted end of the titanium reagent, the latter being the position at which addition to substituted allyltitanium reagents is usually observed. 

Reactions with seven- to nine-membered cydic allylic carbonates or halides give the corresponding cydic allyltitanium compounds. These reagents add to aldehydes and imines with moderate to excellent diastereoselectivities [59]. The allyltitanium compound generated from 1-vinylcyclopropyl carbonate reacts regioselectively with aldehydes and ketones at the less substituted carbon atom to provide alkylidenecydopropane derivatives, as shown in Scheme 13.29 [60], The regiochemical outcome of the reaction can be rationalized by assuming an equilibrium between two allyltitanium spedes that favors the less strained tertiary structure. 

On treatment with (carboxysulfamoyl)triethylammonium hydroxide inner salt methyl ester (Burgess reagent), the adducts of ketones yielded 1-vinylcyclopropyl selenides, but the adducts of aldehydes, e.g. 4, rearranged to cyclobut-1-enyl selenides.176... 

A number of bicyclic ketones such as bicyclo[3.2.1]octa-3,6-dien-2-one which are both a, (3 and y, 6 unsaturated undergo photoisomerization to vinylcyclopropyl ketenes40. These reactions may be mechanistically related to the reactions of 12 and 14 however, the reactions have also been described as [3,3]-sigmatropic shifts41. ... 

New additions to the himachalane class include (213)—(215) Cineraria gei-foliaf and podocephalol (216) Lasianthaea podocephala) Piers et ahave now utilized the Cope rearrangement of /S-(2-vinylcyclopropyl)-a,jS-unsaturated ketones for the construction of jS-himachalene (217) (Scheme 34). 

The bicyclo[S.4.0]undecane sesquitetpenoid ( )-3-himachalene (109) was prepared via a route in which thermolysis of a 3-(2-vinylcyclopropyl) enone played a key role (Scheme 15). Reaction of the P-iodo enone (82) with the stereochemically homogeneous cyclopropylcuprate (106) provides the functionalized trans-divinylcyclopropane (107). Thermolysis of (107) gives exclusively the Cope reanange-ment product (108), which is converted into ( )-P-himachalene (1()9). Notably, in contrast to structurally related systems (vide supra), the p, y-unsaturated ketone function in (108) shows no inclination to rearrange to the corresponding a,P-unsaturated (conjugated) ketone. 

Conjugate addition of vinylcyclopropylcuprate reagents to j8-iodo enones, e.g. to 42 and 46, provides a convenient means of synthesis of cyclic ketones annulated with the cyclohepta-1,4-diene moiety. Where permitted, the initially formed product, e.g. 44, isomerizes into conjugation under the reaction conditions. Thus, enone 45 (n = 1,2) is the only product from the isomerization of fran.9-vinylcyclopropyl enones 43 (R = H). 

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