Cyclopropyl compounds 3 + 2 cycloaddition reactions

Adducts derived from cyclopropyl-TMM reactions are versatile synthetic intermediates. Alkylidenecyclopropanes have been proven useful in further Pd-cata-lyzed transformations [4], On the other hand, vinylcyclopropanes can undergo smooth thermal ring-expansion to cyclopentenes. Thus, a total synthesis of 11-hy-droxyjasionone (27) was achieved with the cyclopropyl-TMM cycloaddition as the crucial step, and the thermal rearrangement of the initial adduct (28) as an entry to the bicyclo[6.3.0]undecyl compound (29), a key intermediate in the synthetic sequence (Scheme 2.9) [19]. 

Cyclopropyl ketones 32 and cyclopropyl imines 33 can also undergo [3+2] cycloaddition reactions with enones 34 in presence of NHC-Ni complexes to afford the corresponding cyclopentane compounds 35 (Scheme 5.9) [11]. The catalytic system is prepared in situ from the use of [Ni(COD),], SIPr HCl salt and KOBu, the reaction also required the use of Ti(O Bu) as an additive to improve yields and increase reactions rates. In most of the cases, th products 35 were obtained in good to excellent diastereoselectivities. 

In intermolecular PET processes, radical ions are formed either as close pairs or as free species from neutral molecules (Sch. 1) [2,6]. Most commonly, carbonyl compounds or related derivatives as for example enol ethers, cyclopropyl ketones, and siloxycyclopropanes are used for intramolecular cyclization reactions. With the exception of cycloadditions the ring-building key step is always an intramolecular bond formation. In PET... 

Disilenes react with ketones, aldehydes, esters and acid chlorides by formal [2 + 21-cycloaddition to yield the corresponding disiloxetanes (equation 73)8,16. The reaction is non-concerted and proceeds through the initial formation of a 1,4-biradical intermediate, as has been shown by the products of reaction of tetramesityldisilene (110) with the cyclopropyl aldehyde 117 (equation 90)163. The absolute rate constants listed in Table 19 indicate there to be a significant difference in reactivity between the monophenyl-substituted disilene 103 and the 1,2-diphenyl-substituted derivatives 104, consistent with a steric effect on the rate of formation of the biradical intermediate. As would be expected, no kinetic deuterium isotope effect is discernible from the relative rates of addition of acetone and acetone- to these compounds. 

Besides the mild conditions and excellent chemo- and regioselectivity the scope of this one-pot coupling-cycloaddition isoxazole synthesis is fairly broad. Due to acid chlorides as halide coupling partners, amines and hydroxy groups inevitably need to be protected prior to the reaction. Therefore, the use of acid chlorides 7 is principally limited to (hetero)aromatic compounds and derivatives without ot-hydrogen atoms. As an exception, the cyclopropyl group is tolerated as a... 

Cyclopropanation of steroids (363) at the 1,2-position with malonate in the presence of potassium t-butoxide and tetramethylguanidine takes place with formation of the di(alkoxycarbonyl)cyclopropane derivatives (364) accompanied by steroidal cyano-alkoxycarbonylcyclopropanes (365). When the reaction is carried without tetramethylguanidine only minor amounts of cyclopropyl steroids are isolated The formation of the cyano compound is explained by an initial nucleophilic displacement of bromine by the tetramethylguanidine moiety, followed by several steps (equation 119). Although the reaction of equation 120 cannot be classified as a MIRC reaction sensu strictu the formation of cyclopropa[c]cinnolines (367) via an intramolecular 1,1-cycloaddition of nitrilimines is mentioned here. Treatment of o-vinylphenyl-substituted chloroglyoxylate... 

The cycloaddition of a diazo compound to an alkyne followed by extrusion of nitrogen under various conditions from an isolated pyrazole represents one of the standard routes to cyclopropenes (Section 3.2.1.1.). In certain cases the reaction is carried out under conditions which might involve direct addition of a carbene derived from the diazo species, e.g. formation of 7, 8, and9. For8(R = cyclopropyl), the product rearranged under the reaction conditions to 1-cyclopropyl-1-trimethylsilylallene. ... 

On the other hand, when tropone (41) is allowed to react with the phosphaalkynes 9a, 9b, or 9 e at a somewhat raised temperature in the molar ratio 1 1 in toluene, the reaction sequence ends with the formation of the diphosphapentacyclic compounds 45a-c [45]. In other words, this means that the initially formed 43 must have undergone a stereoselective, [8 + 2]-cycloaddition with a second equivalent of tropone (41). The hexacyclic species 44 thus formed experience a cyclopropyl-allyl rearrangement with subsequent [1,5]-H shift and ring inversion, finally to furnish the isolated pentacyclic compounds 45 [45]. The semiempirically... 

The reaction of several a-diazoketones with ethyl vinyl ether under various conditions has been examined. In the presence of metal salts [Rh2(OAc)4, Pd(OAc)2, CuCl] ethoxy dihydrofurans are produced. The initial product of this reaction sequence is a cyclopropyl ketone which suffers from a spontaneous rearrangement to the dihydrofuran <96CJC2401>. An efficient synthesis of 3-acylfurans is achieved by Ag(I)/Celite mediated cycloaddition of dicarbonyl compounds with vinyl sulfide (<97TL5671> see also <97TL2095>). A two-step synthesis of 2-substituted 4-furanmethanol compounds was reported. The method involves a Homer-Wadsworth-Emmons reaction between 3-ketophosphonates and l,3-diacetoxy-2-... 

On the basis of the 1,3-dipolar cycloaddition of 5-membered ring carbonyl ylides, syntheses of oxabicyclo[2.2.1]heptan-2-one ring systems were successfully accompUshed. For example, the reactions of the cyclopropyl-substituted five-membered ring carbonyl ylide 48 derived from the a-diazo ketone 47 with different dipolarophiles have been investigated [78-80]. The compound 47 undergoes cycloaddition in the presence of Rh2(OAc)4 with dimethyl maleate, dimethyl fumarate, cyclopentenone, 1,1-dimethoxyethylene and bi-cyclopropylidene furnishing the expected cycloadducts 49-53, respectively... 

Hydrindanes can be synthesized from l,8-dien-3-ynes by [4+2] cycloaddition [30, 219]. However, l,3-dien-8-ynes undergo intramolecular Diels-Alder reactions to give formal [4+2] products or hexahydropentalene compounds [224, 225]. The reaction of cyclopropylenynes gives pentalenes via Prins cyclization (Scheme 1.32) [174]. Due to the lack of stereospecificity in the reaction, anon-concerted opening of the cyclopropyl gold carbene to an open carbocation is proposed. 

The photochemistry of carbonyl compounds has been one of the main areas of research in organic photochemistry for many years. Among aU the different types of carbonyl compounds, P,y-unsaturated ketones have been the subject of extensive studies. The results obtained from these efforts, conducted over a 30-year period, show that, in general, direct irradiation of P,y-unsaturated ketones yields products resulting from 1,3-acyl migration, while triplet-sensitized reactions of these compounds affords cyclopropyl ketones by oxa-di-n-methane (ODPM) rearrangement pathways. Alternative reaction routes, such as decarbonylation, ketene formation, epimerization, [2+2]-intramolecular cycloadditions, Norrish Type I and Norrish Type II reactions, cis-trans isomerizations, and reductions of the C-C double bond, have also been described in some instances, depending on some particular structural features present in the P,y-unsaturated ketone. However, the photoreactivity of these compounds is dominated by the two main processes mentioned above. 

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