Propargyl esters cycloaddition

Azomethine ylides of pyrrolo[l,2- ]pyrazine <1996JOC4655> and 3,4-dihydro pyrrolo[l,2-tf]pyrazine <1997T9341> undergo 1,3-dipolar cycloadditions with a number of dipolarophiles. For example, the ylide 178 reacts with propargylic ester 179 to give the tricyclic derivative 180 (Equation 43). 

Table 4 1,3-Dipolar cycloaddition of propargyl esters 86 to sydnone 85 (Scheme 3) <2006H1007, 2006SL901 >...

Cycloaddition reactions of a,/3-unsaturated chromium and tungsten complexes have been studied to a great extent and have been reviewed.3 -6 Our report on cycloaddition of (l-alkynyl)carbene complexes is restricted to a short abstract and an update including more recent results. A most remarkable feature of [4+2] cycloadditions of 1,3 dienes to C=C bonds of (l-alkynyl)carbene complexes, e.g., li, is that such reactions proceed under very mild conditions, compared to those for reactions of propargylic esters, e.g., 41. Thus, formation of a Diels-Alder adduct, e.g., a norbornadiene derivative 42, can be achieved at 25°C via carbene complexes instead of at 190°C via the direct route (Scheme 15).68 Ligand disengagement from compound 40 can be achieved in various ways, e.g., by formation of an ester 43 through oxidation of the Cr=C bond, or by formation of an allyl silane 4369 or a stannane.70 71... 

The tandem cyclization-cycloaddition reaction of 1-diazoacetyl-7,7-dimethylbicyclo[2.2.1]heptan-2-one (1) with dimethyl butynedioate catalyzed by rhodium(II) acetate dimer in benzene at 25 °C, afforded a formal [3 + 2] cycloadduct 2 in 85% yield with complete diastereofacial selectivity48. This reaction is interpreted to proceed via rhodium carbenoids and subsequent transannular cyclization of the electrophilic carbon onto the adjacent oxo group to generate a cyclic carbonyl ylide. followed by 1,3-dipolar cycloaddition. Similar reactions are observed with other dipolar-ophiles, such as propargylic esters and A -phenylmaleimide. Studies dealing with the geometric requirements of dipole formation were undertaken. 

A fascinating approach to the synthesis of pyridine heterocycles has been discovered by using (arene)Fe(O) complexes to catalyze [2+2+2] cycloaddition reactions. The proposed method consists of a cross cyclization of alkynes and nitriles [45]. An example of such a reaction is depicted in Scheme 25. In the presence of (Ty -l,5-cyclooctadiene)(Ty -phosphinine)Fe(0) 85, butyronitrile 86 combines with two molecules of methyl propargyl ester 87 yielding a mixture of isomeric pyrroles 88 and 89. The reaction proceeds at ambient temperature, but relatively long reaction times are required to obtain good yields. The symmetric... 

With a combination of Cu(OTQ2 and a chiral tridentate P,N,N-ligand as the catalyst, the copper-catalyzed asymmetric [3 + 2] cycloaddition of P-ketoesters with propargylic esters was developed for the synthesis of optically active 2,3-dihydroflirans bearing an exocyclic C=C bond at C-5, in high yield and enantioselectivity (14AGE10223). 

Recently, Chen and coworkers reported an efficient new method to construct a series of densely functionalized 4,5-dihydro-IH-azepine products 41 from the intermolecular reaction of alkyl azides with propargylic esters. In this approach, sequential reaction of vinyl-gold carbenoids 42 with allqrl azides and formation of vinyl imine intermediates 43 may be involved fScheme 4.14). Then a subsequent formal [4+3] cycloaddition with another molecule of vinyl-gold carbenoid 42 afford the desired azepine 41. 

A gold-catalysed 3 + 2-cycloaddition-hydrolytic Michael addition-retro-aldol reaction of propargyl esters tethered to cyclohexadienones gives tetrahydrofuranones, diox-atricycloundecenones, and furofurans (Scheme 112). The product cyclohexenones or cyclohexanones with a y-quaternary centre result from multiatom transpositions... 

Liming Zhang of the University ofNevada, Reno devised J. Am. Chem. Soc. 2008,130, 3740) a new route to oxygenated dienes such as 22, based on Au-catalyzed rearrangement of a propargylic ester such as 21. Note that the oxygen has shifted to the adjacent carbon in the course of this transformation. The product dienes participated smoothly in Diels-Alder cycloaddition. 

A gold-catalyzed [3,3] rearrangement of propargyl ester 240 to carboxyallene 241 followed by further activation by the Au catalyst affords W-shaped gold allylic cation 242. Cation 242 then undergoes intramolecular cycloaddition via an endo (compact) transition structure 243 to give gold... 

The Brpnsted acid-mediated formal 3 + 3-cycloaddition reaction of /i-enaminones with cf, -unsaturated aldehydes formed tetrahydroquinolinones. The Yb(NTf2)3-catalysed 3 + 3-cycloaddition reaction of isatin ketonitrones (122) and cyclopropanes (123) yielded spiro[tetrahydro-l,2-oxazine]oxindoles (124) in moderate to good yields and good regioselectivities (Scheme 38). The Cu-catalysed 3 + 3-cycloaddition reaction of propargyl esters with cyclic enamines yielded chiral e r/o-adducts with bicyclo[ .3.1] frameworks. The catalyst was prepared by the combination of Cu(0Ac)2 H20 with a chiral tridentate ferrocenyl-PA(,(V-ligand. The cationic... 

Two different types of tandem reactions for the synthesis of highly functionalized cyclohexenones cyclopropyl-substituted propargyl esters initiated rhodium-catalysed Saucy-Marbet 1,3-acyloxy migration have been reported (Scheme 152). The resulting cyclopropyl-substituted allenes derived from acyloxy migration followed by 5 -f 1-cycloaddition with carbon monoxide. ... 

A Rh-catalysed [Rh(CO)2Cl]2 1,3-acyloxy migration of a propargyl ester followed by intramolecular 4 + 2-cycloaddition of the vinylallene and unactivated alkyne has been reported to give cyclohexenones (Scheme 155). ° ... 

A family of interesting polycychc systems 106 related to pyrrolidines was obtained in a one-pot double intermolecular 1,3-dipolar cycloaddition, irradiating derivatives of o-allyl-sahcylaldehydes with microwaves in toluene for 10 min in presence of the TEA salt of glycine esters [71]. A very similar approach was previously proposed by Bashiardes and co-workers to obtain a one-pot multicomponent synthesis of benzopyrano-pyrrolidines 107 and pyrrole products 108 (Scheme 37). The latter cycloadducts were obtained when o-propargylic benzaldehydes were utihzed instead of o-allyhc benzalde-hydes, followed by in situ oxidation [72]. 

Takasu, Ihara and coworkers described an efficient synthesis of ( )-paesslerin A (4-73) using a combination of a [4+2] and a [2+2] cycloaddition (Scheme 4.16) [25], Reaction of 4-71 and propargylic acid methyl ester in the presence of the Lewis acid EtAlCl2 led to 4-72 in 92 % yield, which was converted in six steps into the desired natural product 4-73 by transformation of one of the ester moieties into a methyl group, hydrogenation of one double bond, removal of the other ester moiety, and exchange of the TIPS group for an acetate. 

Scheme 6.186) [347]. The condensation of O-allylic and O-propargylic salicylalde-hydes with a-amino esters was carried out either in the absence of a solvent or - if both components were solids - in a minimal volume of xylene. All reactions performed under microwave conditions rapidly proceeded to completion within a few minutes and typically provided higher yields compared to the corresponding thermal protocols. In the case of intramolecular alkene cycloadditions, mixtures of hexa-hydrochromeno[4,3-b]pyrrole diastereoisomers were obtained, whereas transformations involving alkyne tethers provided chromeno[4,3-b]pyrroles directly after in situ oxidation with elemental sulfur (Scheme 6.186). Independent work by Pospisil and Potacek involved very similar transformations under strictly solvent-free conditions [348]. 

Other variations of the [3 + 2] cycloaddition chemistry involving either SO2 or a S2O equivalent have been explored (Scheme 47). Iron allenyl complexes undergo reaction with SO2 to give either vinyl iron (105) or (106), depending on the substitution pattern. A propargylic iron complex reacts in a similar manner to give (107), but reacts with a cyclic thiosulfinate ester to give (108). 

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