Allenes hetero

A regio- and diastereoselective Pd-catalyzed domino silastannylation/allyl addition of allenes 6/1-236 containing a carbonyl moiety with Bu3Sn-SiMe3 6/1-237 is described by Kang and coworkers [117]. The reaction allows the synthesis of hetero-and carbocyclic compounds with a ring size of five and six. It can be assumed that... 

Weinreb86 has reported the Alder-ene cyclization of enallenes under thermal conditions (Equation (85)). Varying the substitution pattern of alkene and allene groups had little effect on the yield of cyclized product. One exception was a,/ -unsaturated ester 130(Equation (86)) cycloisomerization under thermal conditions led to the formation of the Alder-ene product 131 and the unexpected hetero-Diels-Alder product 132 in a 3 1 ratio. 

The unsymmetricall allene 189 dimerized to give pyranopyran 190. A hetero-Diels-Alder reaction was followed by the subsequent electrocydic ring closure reaction [8]. 

Electron-deficient allenes also undergo hetero-Diels-Alder reactions. N,N-Dimethyl-hydrazones 193 reacted with allenedicarboxylate 110a in refluxing acetonitrile to give 2-carboxy-3-pyridineacetic acid diesters [157]. 

The anodic oxidation of substituted allenes [76-79] and hetero-allenes [80-85] has been extensively studied by Becker and coworkers. Oxidation of secondary and tertiary alkyl isothiocyanates resulted in an ot-cleavage processes [77]. Primary alkyl isocyanates yielded amides and carbonyl compounds due to the nucleophilic involvement of either acetonitrile or water [80]. Primary alkyl isothiocyanates 48 afforded five-membered thiadiazolidine 49 and 50 and... 

We dealt with [4+2]-cycloadditions very briefly in Section 3.3.1. As you saw there, a [4+2]-cycloaddition requires two different substrates one of these is an alkene—or an alkyne—and the other is 1,3-butadiene or a derivative thereof. The reaction product, in this context also called the cycloadduct, is a six-membered ring with one or two double bonds. Some hetero analogs of alkenes, alkynes, and 1,3-butadiene also undergo analogous [4+2]-cycloadditions. In a [2+2]-cycloaddition an alkene or an alkyne reacts with ethene or an ethene derivative to form a four-membered ring. Again, hetero analogs may be substrates in these cycloadditions allenes and some heterocumulenes also are suitable substrates. 

The array of dienophiles amenable to these hetero Diels-Alder reactions is not limited to enol ethers and enamines since allylsilanes and simple alkenes have also been successfully employed [370, 371]. More recently, it has been shown that methoxy allenes such as 4-41 undergo formation of 6H-l,2-oxazines 4-43 upon cycloaddition to nitrosoalkenes such as 4-34 and subsequent tauto-merisation of the intermediate exo-methylene compound 4-42 (Fig. 4-9) [372, 373]. In these studies, 4-43 proved to be a versatile synthetical intermediate allowing oxidative demethylation or reductive removal of the methoxy group as well as nucleophilic substitutions after the generation of an azapyrylium ion [372 - 374]. Furthermore, ring contraction reactions of these oxazines leading to pyrroles [373] and y-lactames [375] are known. 

In a similar manner, Grigg and co-workers have demonstrated that a combination of 102, allene and a nucleophile (YH2) affords hetero- or carbocycles in the presence of palladium(O) [92], Presumably, insertion of aryl iodide to allene gives a jr-allyl intermediate 103, intercepted by a nucleophile (YH2), the latter being trapped by addition onto the Michael acceptor to furnish hetero- or carbocycles 105 (Scheme 40). 

The reaction of enamines and imines with acrylamide results in aza-annulation120,121. Other electrophilic alkenes which have been used to alkylate enamines and the products used in hetero- or carbocyclic synthesis include ethyl / -nitroacrylate122, where reaction occurs beta to the nitro not the ester group, 2-(phenylseleno)prop-2-enenitrile [CH2 = C(SePh)CN]123,124, phenyl a-phenylselenovinyl sulphone [CH2 = C(SePh)-S02Ph]124 and phenyl a-bromovinyl sulphone124. An electrophilic allene, phenylsulpho-nylpropadiene, has also been used to alkylate enamines125 (Scheme 44). 

Nina A. Nedolya was born in Irkutsk (Russia) and educated in organic chemistry at the Irkutsk State University (Diploma 1972, PhD 1982, DSc 1998). From 1995 to 1999 she was associated with Prof. L. Brandsma at the Utrecht University (The Netherlands). In 1999 she obtained her second PhD from the Utrecht University. She is presently Head of the Research Group of Chemistry of Heterocyclic Compounds at A. E. Favorsky Irkutsk Institute of Chemistry. She is the author of over 210 review articles and research papers. She is also one of the inventors for 112 patents. She is interested in the chemistry of polyfunctional unsaturated heteroatomic systems (vinyl, allenyl, and alkynyl ethers and their derivatives, linear and cyclic heteropolyenes, hetero-cumulenes), including synthesis of important heterocycles, particularly pyrroles, thiophenes, thiazoles, imidazoles, dihydrofurans, dihydropyridines, pyridines, quinolines, dihydroazepines, and azepines, based on metallated allenes or alkynes and/or heterocumulenes. 

Mechanistically, this new insertion-CI-Diels-Alder hetero domino sequence can be rationalized as follows (Scheme 64) After the oxidative addition of the aryl halide 115 or 118 to the in situ generated Pd(0) species the arylpalladium halide 120 intramolecularly coordinates and inserts into the tethered triple bond via a syn-carbopaUadation to furnish cyclized vinylpalladium species 121 with a p-acceptor substitution in a stereospecific fashion. Transmetallation of the in situ generated copper acetylide 122 gives rise to the diorganylpalladium complex 123 that readily undergoes a reductive elimination and liberates the electron poor vinylpropargylallyl ether 124. The triethylamine catalyzed propargyl-allene isomerization furnishes the... 

Blechert has developed an interesting synthesis of 2-substituted indoles which involves the conjugate addition of V-phenylhydroxylamine salts (or V-phenylnitrones) to electron-deficient allenes, followed by carbanion-accelerated hetero-Cc rearrangement of the Michael adduct. For exanple, addition of the hydroxylamine salt (46) to the allenyl sulfone (47) produces the anion (48), which undergoes rapid 3.3-sigmatropic rearrangement to afford the -keto sulfone (49). Cyclization to the indole proceeds smoothly upon exposure to formic acid (Scheme 3). 

Larock, R. C., Zenner, J. M. Enantioselective, Palladium-Catalyzed Hetero- and Carboannulation of Allenes Using Functionally-Substituted Aryl and Vinylic Iodides. J. Org. Chem. 1995, 60, 482-483. 

The reaction of aryl halides with copper(I) alkynides is known as the Castro reaction (equation 3). The reaction has proved to be particularly important in the synthesis of a wide range of tolan and hetero-aromatic alkynes. Vinyl and allenic halides"" can also be used and several reviews of the reaction have been published. " ... 

A carbanion -accelerated hetero-Cope rearrangement was reported by Blechert 170). Reaction of the sodium salt of the hydroxamic acid (202) with the allene sulfone 203 led at 0 °C within 10 min to 206. Undoubtedly, the carbanions 204 and 205 are the important intermediates in this transformation. A carbanion -accelerated... 

The methods for generating acyl ketenes (Scheme 7-V) and their subsequent in situ participation in [4 + 2] cycloadditions with a wide range of hetero- or olefinic and acetylenic dienophiles (Scheme 7-VI), including acyl ketenes,185 186,197 carbonyl compounds, 86-188 nitriles,1874,189,191 isocyanates and isothiocyanates,1864,190,191 ketenes,191 imines,1864,1874,191,192 carbo-diimides,l87c 190,191,193 ynamines,194 ketene acetals,1864,195 enol ethers,1864,191,196 and V-sulfinylamines197 have been extensively reviewed.5,9,12 Two reports have detailed the 4-n- participation of allenic ketones in [4 + 2] cycloaddition reactions [Eq. (51)].198,199... 

On substitution of the two CRj groups in the allene molecule by isoelectronic hetero groups or atoms X and Y (X, Y = O, S, NR), molecules X=C=Y are formed, which are called pseudo- or hetero-allenes. This chapter deals with the heteroallenes CSj and COS and the ligands based on these two molecules, the heteroallyls. The heteroallenes themselves have been reviewed by Gattow and Behrendt and Reid respectively. Their coordinating properties have been compared recently by Ibers. Assuming X to be preferred over Y for coordination, both end-on coordination by X and side-on ( / ) coordination by the C=X double bond occurs, whereas for X=Y=S bridging coordination between two metals is also found. 

The nickel-iminophosphine-catalysed 4- -2-cycloaddition of enones with allenes formed highly substituted dihydropyrans. The enantioselective amine-catalysed 4-I-2-cycloaddition of allenoates with oxo-dienes produced polysubstituted dihydropyrans in high yields and with high enantioselectivities. Novel enam-ine/metal Lewis acid bifunctional catalysis has been used in the asymmetric inverse-electron-demand hetero-Diels—Alder reactions of cyclic ketones with Q ,j9-unsaturated a-ketoesters. The 4- -2-cycloaddition of acylketenes (80) with 2-unsubstituted and 2-monosubstituted 3-aryl-2//-azirines (81) produced 1 1 (82) or 2 1 (83) adducts, being derivatives of 5-oxa-l-azabicyclo[4.1.0]hept-3-ene or 5,7-dioxa-l-azabicyclo[4.4.1]undeca-3,8-diene. The formation of the monoadducts proceeds via a stepwise non-pericyclic mechanism (Scheme 25). A-heterocyclic carbene-catalysed 4- -2-cycloaddition of ketenes with 1-azadienes yielded optically active 3,4-dihydropyrimidin-2-ones (93% ee) ... 

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