Allenyl groups reactions

Very recently, Cook and Danishefsky [24] reported an interesting regioselectivity of intramolecular Diels-Alder reactions reversed by the change in the dienophihc moieties from vinyl to allenyl group (Scheme 19). For R = 2-propenyl group, C is bonded to the methyl substituted carbon Cj of the cyclohexadienone ring. For R = 2,3-butadienyl, C is bonded to Cy... 

Allenylcobaloximes, e.g. 26, react with bromotrichloromethane, carbon tetrachloride, trichloroacetonitrile, methyl trichloroacetate and bromoform to afford functionalized terminal alkynes in synthetically useful yields (Scheme 11.10). The nature of the products formed in this transformation points to a y-specific attack of polyhaloethyl radicals to the allenyl group, with either a concerted or a stepwise formation of coba-loxime(II) 27 and the substituted alkyne [62, 63]. Cobalt(II) radical 27 abstracts a bromine atom (from BrCCl3) or a chlorine atom (e.g. from C13CCN), which leads to a regeneration of the chain-carrying radical. It is worth mentioning that the reverse reaction, i.e. the addition of alkyl radicals to stannylmethyl-substituted alkynes, has been applied in the synthesis of, e.g., allenyl-substituted thymidine derivatives [64],... 

Allenyl- and propargyl-phosphonium salts have also been used as precursors of heterocyclic compounds in the presence of various functionalized nucleophiles279, via the intermediacy of vinylphosphonio compounds however, an ylide extrusion has been sometimes observed815,816, depending on the nature of the functions in the nucleophile (reaction 250). Allenylphosphonium salts are able to add such weak CH acids as in ketones, even in absence of basic catalysts817,818, without any modification of the keto group (reaction 251). 

As already discussed above several C-nucleophiles also add smoothly to y-lactols (Eq. 85, Table 9). BF3 is the promotor of choice allowing efficient and highly diastereo-selective reactions with allyl and cyanotrimethylsilane or with bis(trimethylsilyl)ace-tylene which introduce the corresponding substituents at C-5 of the methyl tetra-hydrofuran-3-carboxylates 204, In the case of propargyltrimethylsilane an allenyl group is transferred to the heterocyclic 93). 

C. Reactions of Cluster-Bound Allenyl Groups I. Adduct Formation... 

Kitagawa. O., Suzuki, T., Fujiwara, H., Fujita, M., and Taguchi, T., Alkaline metallic reagent-catalyzed hydrocarbocyclization reaction of various active methine compounds having an unactivated 4-aIkynyl or allenyl group. Tetrahedron Lett., 40, 4585, 1999. 

Pauson-Khand reaction of alkynyl ketones in which an allenyl group is extended further from the a -position is intriguing. It has been found that one of the double bonds of the allene unit can be selected to participate by using certain transition metal catalysts besides modification of the substrates. ... 

Hydroamination. Formation of the A-Boc derivative of 3-vinyl-5-phenylisoxazoli-dine from an O-alkylhydroylamine that contain a p-allenyl group paves the way toward elaboration of sedamine. The intramolecular hydroamination is a high-yielding reaction. 

CycUzations. Activation of an allenyl group with SnCLt and linkage to a C-nucleophile constitute a ring formation process. The reaction of Al-arylaldimines with allylsilanes (or allylgermanes) in the presence of SnCl, leads to 2,4-disubstimted 1,2,3,4-tetrahydro-quinolines due to rapid interception of the carbocationic intermediates. 

We have also observed that under the catalysis of Pd(PPh3)4, the reaction of 3,4-allenyl toluenesulfonamides with aromatic halides afforded 2,3-dihydro-pyrroles 41 or a mixture of vinylic azetidines and 1,2,3,6-tetrahydropyridines, depending on the substituent at the 3 position of the 3,4-allenyl group (Scheme 18)... 

Hydrocarbocyclization reactions of various active methine compounds having an unactivated 4-alkynyl or allenyl group, to form methylenecyclopentane derivatives in good yields, have been promoted catalytically by NaH or n-BuLi without the assistance of a transition metal. ... 

Additionally, in this case, the ratio of prototropic isomerization of the allenyl group to the propargylic moiety dramatically increases and the yields of propargylic derivatives grow with decrease of the reaction temperature (37% at -80°C) (Scheme 2.223). 

The reaction of the o-iodophenol 275 with an alkylallene affords the bcnzo-furan derivative 276[184], Similarly, the reactions of the 6-hydroxyallenes 277 and 279 with iodobenzene afford the tetrahydrofurans 278 and 280. Under a CO atmosphere, CO insertion takes place before the insertion of the allenyl bond, and a benzoyl group, rather than a phenyl group, attacks the allene carbon to give 280. Reaction of iodobenzene with 4,5-hexadienoic acid (281) affords the furanone derivative 282[185]. 

In addition to alcohols, some other nucleophiles such as amines and carbon nucleophiles can be used to trap the acylpalladium intermediates. The o-viny-lidene-/j-lactam 30 is prepared by the carbonylation of the 4-benzylamino-2-alkynyl methyl carbonate derivative 29[16]. The reaction proceeds using TMPP, a cyclic phosphite, as a ligand. When the amino group is protected as the p-toluenesulfonamide, the reaction proceeds in the presence of potassium carbonate, and the f>-alkynyl-/J-lactam 31 is obtained by the isomerization of the allenyl (vinylidene) group to the less strained alkyne. 

The 1,3-dipoles consist of elements from main groups IV, V, and VI. The parent 1,3-dipoles consist of elements from the second row and the central atom of the dipole is limited to N or O [10]. Thus, a limited number of structures can be formed by permutations of N, C, and O. If higher row elements are excluded twelve allyl anion type and six propargyl/allenyl anion type 1,3-dipoles can be obtained. However, metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions have only been explored for the five types of dipole shown in Scheme 6.2. 

Kanematsu s group used a combination of an intramolecular [2+2] cycloaddition of an allenyl ether 4-202 followed by a [3+3] sigmatropic rearrangement (Scheme 4.44) [70]. The substrate for the domino reaction can be obtained in situ by treat-... 

Arylative or silylative cyclizations of allenyl aldehydes or ketones have been reported (Equations (101) and (102)).459,459a The intermolecular process, that is, three-component coupling reaction of aldehydes, allenes, and arylboronic acids, is catalyzed by palladium as well (Equation (103)).46O 46Oa These reactions are proposed to proceed through nucleophilic attack of the allylpalladium intermediates to the carbonyl groups. 

A new type of asymmetric hydrosilylation which produces axially chiral allenylsilanes has been reported by use of a palladium catalyst coordinated with the bisPPFOMe ligand 51b.64 The hydrosilylation of l-buten-3-ynes substituted with bulky groups such as tert-butyl at the acetylene terminus took place in a 1,4-fashion to give allenyl(trichloro)-silanes with high selectivity. The highest enantioselectivity (90% ee) was observed in the reaction of 5,5-dimethyl-T hexen-3-yne with trichlorosilane catalyzed by the bisPPFOMe-palladium complex (Scheme 13). 

The competition between a propargylic ether and a teriary propargyhc amine provided an allenyl ether rather than an allenylamine [182], The reaction was also successful with propargyl allyl ethers [232]. An additional ester group in the propargylic position is tolerated [233], and consequently the reaction also works with esters of propargyhc alcohols [234—236]. In the past 4years, several derivatives of carbohydrates were converted successfully [217, 237-241] two examples are the isomeriza-tions of enantiomerically pure 98 [242] and 100 [217, 243] (Scheme 1.43). 

An analogous mechanism was proposed for the conversion of the triflate 416 to the vinyl-, allyl- and allenyl-A2-cephems 448 in yields of 47-71% by the respective tributyltin compounds in the presence of cuprous chloride (Scheme 6.91) [176]. Accordingly, the cyclic allene 417 should be liberated from 416 in the first step. Then, the organocopper species would transfer a hydrocarbon group to the central allene carbon atom of 417, leading to an allyl anion derivative, which is protonated during the workup. These reactions of 416 and 443 indicate that the cyclic allenes 417 and 444 behave toward nucleophiles as 1,2-cyclohexadiene (6) (Schemes 6.11— 13) and its non-polar derivatives such as 215 (Scheme 6.51), 221 (Scheme 6.52), 311 (Scheme 6.67) and 333 (Schemes 6.71 and 6.73), that is, they interact with nucleophiles at the central carbon atom of the allene system exclusively. 

---