Furans Diels-Alder

Synthesis of multisubstituted furan rings using silyl protection 99CSR209. Synthetic applications of furan Diels-Alder chemistry 97T14179. Transformation of furans to N-heterocycles by aza-Achmatovicz reaction 98SL105. 

Apart from cydopentadiene 309a, furan [151, 165, 321-323, 327, 329] and pyrrole derivatives [158, 325] 309b and 309c, respectively, are also often used as dienes. Recently, the synthetic applications of furan Diels-Alder chemistry were reviewed comprehensively [330]. In the case of a,/3-unsaturated hydrazones 312, isomerization and elimination of dimethylamine convert the Diels-Alder products 314, which... 

Evans, D. A. Barnes, D. M. Cationic bis(oxazo-line)Cu(Il) Lewis add catalysts. Enantioselec-tive furan Diels-Alder reaction in the synthesis of ent-shikimic acid. Tetrahedron Lett. 1997, 38, 57-58. 

C. O. Kappe, S. S. Murphree, A. Padwa, Synthetic Applications of Furan Diels-Alder Chemistry Tetrahedron 1997, 53 14179-14231. 

A multi-gram enantioselective synthesis of (+)-37, a key precursor to the tetracycline antibiotics, has been performed from simple heterocyclic compounds. Key steps in the route involve enantioselective addition of divinylzinc to 3-benzyloxy-5-isoxazolecarboxaldehyde (with 93% ee) for the preparation of 36 and, after its nucleophilic addition to 35, an intramolecular furan Diels-Alder cycloaddition <07OL3523>. 

Examples of the exploitation of furan Diels-Alder cycloadditions for the construction of complex systems are many one delightful example is shown below. The residual dienophihc double bond of the Diels-Alder adduct between one of the two furan rings and dimethyl acetylenedicarboxylate then enters into cycloaddition with the second furan ring. ... 

Synthetic applications of furan Diels-Alder chemistry , Kappe, C. O., Murphree, S. S. and Padwa, A., Tetrahedron, 1997, 55, 14179. 

Knight - Vinyl furan Diels-Alder reactions [88TL2107]... 

Furan also undergoes cycloadditions with allenes and even with simpler dienophiles, like acrylonitrile and acrylate (specifically enhanced by the presence of zinc iodide),and with maleate and fumarate esters, if the addition is conducted under high pressure. This device can also be used to increase markedly the reactivity of 2-methoxy- and 2-acetoxyfuran towards dienophiles. Lewis acid catalysis can also been used to accelerate furan Diels-Alder additions. At higher reaction temperatures alkynes and even electron-rich alkenes will add to furan. 

Yeo W-C, Chen S, Tan G-K, Leung P-H (2007) Synthesis of P-chiral phosphines via chiral metal template promoted asymmetric furan Diels-Alder reaction. J Organomet Chem 692 2539-2547... 

When the dichloro diaryl ether 112 was treated with x-BuIi, a dibenzyne was generated and subsequently trapped by 2-methoxyfuran, affording dinaphthyl ethers 113 and 114 after aromatization (Scheme 12.34) [64]. The monocycloadducts 115 and 116 were also present in the reaction mixture. With carefijl control of the stoichiometry of the butyl lithium, an iterative double benzyne-furan Diels-Alder reaction was achieved between benzyne precursor l,4-difluoro-2,5-dime-thoxybenzene and two different furans. 

Following the same concept, Akai et al. have used the bulky and robust TBS group for controlling theregioselectivity of aryne-furan Diels-Alder reactions. Thus, 3-TBS-arynes react with a wide variety of substituted furans to give preferentially the and-adducts 16, which become the only isomers observed (anti/syn> 50/1) when the C-2 substituent of the furan is also a relatively bulky group (f-Bu, TMS, or SnBUj). Interestingly, this reaction saves as a method for the selective synthesis of substituted 1-naph-thol derivatives 17 by treatment of and-adducts 16 with p-toluenesulfonic acid (Scheme 12.11) [19]. 

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