Hetero with dimethyl acetylenedicarboxylate

As already described for the all-carbon-Diels-Alder reaction, a hetero-Diels-Alder reaction can also be followed by a retro-hetero-Diels-Alder reaction. This type of process, which has long been known, is especially useful for the synthesis of heterocyclic compounds. Sanchez and coworkers described the synthesis of 2-aminopyridines [48] and 2-glycosylaminopyridines 4-144 [49] by a hetero-Diels-Alder reaction of pyrimidines as 4-143 with dimethyl acetylenedicarboxylate followed by extrusion of methyl isocyanate to give the desired compounds (Scheme 4.30). This approach represents a new method for the synthesis of 2-aminopyridine nucleoside analogues. In addition to the pyridines 4-144, small amounts of pyrimidine derivatives are formed by a Michael-type addition. 

Substituted 4,5-dihydroazepines 321 (e.g., R1 = Bn, R2 = R3 = H, R4 = M e 82% yield) may be prepared in high yield by a rhodium-mediated hetero-[5+2]-cycloaddition of the cyclopropyl imines derived from 318 on reaction with the primary amines 319, with dimethyl acetylenedicarboxylate 320 (Equation 48) <2002JA15154>. 

A number of selenium heterocycles are prepared utilizing carbon-selenium double bonds as 271 dienophilic intermediates for [4+2] cycloadditions. However, Koketsu et al. reported a novel hetero Diels-Alder reaction wherein selenoazadienes 353 serve as 47t components. Accordingly, compound 353 reacts with dimethyl acetylenedicarboxylate to yield 4-selenazolone 354. The proposed mechanism involves the formation of hetero Diels-Alder adduct 355, which is converted into 4-selenazolone 354 following purification on silica gel. Protonation of cycloadduct 355 presumably affords the selenoamidine 356, which is converted into 357 by nucleophilic recyclization <03H(60)1211>. 

Hetero Diels-Alder reactions of selenazadienes with dimethyl acetylenedicarboxylate yield 4-selenazolones 13, 53. Interestingly, the reaction does not give the expected Diels-Alder adduct but instead a separable mixture of EjZ isomers of a 4-selenazolone 13, 53 is obtained (Scheme 16) <2003H(60)1211>. 

The enamino dithiocarboxylate 367 (R = H), acting as hetero-diene was reacted with dimethyl acetylenedicarboxylate in DMF at 150 °C to give the corresponding benzothiapyran 500. The reaction proceeded through the formation of a cycloadduct that upon loosing an aniline moiety gave 500 (91JHC1245) (Scheme 108). 

A hetero-fused 1,2,4-triazine (457) has been prepared by reaction of 6,7-dimethoxy-2//-l,3-benzothiazine (456) with dimethyl acetylenedicarboxylate and dimethyl azodicarboxylate (Equation (62))—a [2 -I- 2 -f 2] combination <82H(19)489>. 

A variety of cyclic phosphonium ylide structures have been reported. Hetero-cyclic and -bicyclic structures, including the ylide (11) and a variety of iminophosphoranes, are the products of the reaction of the 1,2-dihydro-1,3,2-diazaphosphinine (10) with dimethyl acetylenedicarboxylate. Attempts to prepare a simple adduct of DBN with the (phosphino)(P-chlorophosphonio) carbene (12) led instead to formation of the unsaturated tricyclic adduct (13). The diphosphete structure (14) is the product of a simple two component reaction of dichloro(bis(trimethylsilyl)methylphosphine) with DBU. Details of the synthesis, chemistry and structure of X -phosphetes (15), benzo-X, -phosphetes (16), and naphtho-X -phosphetes (17) have been reported. 2,4-Diphosphoniodihydro-phosphetide cations (19) have been prepared by condensation of the... 

Wender et al. reported that the rhodium-catalyzed hetero-[5 + 2]-cycloaddition of the cyclopropyl imines 446 and dimethyl acetylenedicarboxylate gave the dihydroazepines 447 in high yields (Scheme 141).202 The rhodaheterocycle intermediate 448 is formed upon treatment of 446 with the rhodium catalyst, which undergoes insertion of the alkyne to give 449, and finally the reductive elimination of Rh gives 447. 

Atroposelective cycloaddition reactions of A-2-(r-butylphenyl)- and A-2,5-(di-r-butylphenyl)-maleimide show good to excellent stereoselectivities and the high rotation barriers prevent cycloadducts from interconverting. The stereospeciflc hetero-Diels-Alder reaction of o-quinone methides (80) with o-quinones (79) in MeOH at room temperature produce the 4a,8-di(hydroxymethyl)chromane derivatives (81) and (82) in high yields (Scheme 29). The intramolecular inverse-electron-demand Diels-Alder reaction of o-quinone methides (84) derived from 2-(l-hydroxy-5-alkenyl)phenol derivatives (83) produces l,2,3,3a,4,9b-hexahydrocyclopenta[c][l]benzopyrans (85) under mild acidic conditions (Scheme 30). The Diels-Alder reactions between dimethyl-cyclohexadiene derivatives and di-(-)-menthyl acetylenedicarboxylate exhibit modest diastereoselectivity. ... 

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