Studies on Nitration of Furan Derivatives. Part II. On the Nitration of Furfurylidene-type Compounds
作者:Tadashi Sasaki
DOI:10.1246/bcsj.27.398
日期:1954.7
The nitration, by using both fuming nitric acid mixed with acetic anhydride and fuming nitric acid alone, was carried out on 13 kinds of furfurylidene compounds, C4H3O–CR1R2. (1) These furfurylidene-type compounds in which R1 and R2 are electro-groups are stable against both acidic reagents and can be nitrated without formation of the nitration intermediate. (2) In the case qf a group being—CHO or—COCH3
Diels−Alder Reaction of 2-Amino-Substituted Furans as a Method for Preparing Substituted Anilines
作者:Albert Padwa、Martin Dimitroff、Alex G. Waterson、Tianhua Wu
DOI:10.1021/jo9702599
日期:1997.6.13
5-Amino-2-furancarboxylic acid methyl ester undergoes a facile Diels-Alder cycloaddition with a variety of dienophiles to afford ring-opened cycloadducts that are readily dehydrated using BF3 . OEt2 to give polysubstituted anilines. In each case, the cycloaddition proceeds with high regioselectivity, with the electron-withdrawing group being located ortho to the amino group. The most favorable FMO interaction is between the HOMO of the furanamine and the LUMO of the dienophile. The atomic coefficient at the ester carbon of the furan is larger than that at the amino center, and this nicely accommodates the observed regioselectivity. The [4 + 2]-cycloaddition of N-(5-nitrofuranyl)morpholine with methyl vinyl ketone affords a mixture of three phenols. One of the phenols is derived from a Diels-Alder reaction followed by nitro group ejection and subsequent aromatization. The remaining two phenols are the result of cleavage of the initially formed oxabicyclic intermediate with concomitant migration of the nitro group. The mild reaction conditions with which furan-2-carbamic acid tert-butyl ester undergoes Diels-Alder cycloaddition with N-phenylmaleimide allow for the ready isolation of the initial oxybridged cycloadduct.
IMDAF Cycloaddition as a Method for the Preparation of Pyrrolophenanthridine Alkaloids
作者:Albert Padwa、Martin Dimitroff、Alex G. Waterson、Tianhua Wu
DOI:10.1021/jo980008f
日期:1998.6.1
Acylation of 5-amino-2-furancarboxylic acid methyl ester with alkenoyl acid chlorides gives 2-amidofurans that undergo intramolecular Diels-Alder cycloadditions. The reactions occur at 165 degrees C in toluene or at 100 degrees C when 4 M ethereal LiClO4 was used as the solvent. The resultant dihydroindoles are formed by the nitrogen lone pair assisted ring opening of the initial era-bridged cycloadducts, followed by loss of water. Under certain conditions, alternative cationic cyclization routes become important pathways. Several members of the pyrrolophenanthridine class of alkaloids were obtained by a short, efficient method based on the intramolecular Diels-Alder furan cycloaddition of 2-amidofurans containing a tethered alkenyl group. The resulting dihydroindoles were elaborated in one step to the 1H-pyrrolo[3,2,1-de]phenanthridine ring system by a free radical induced cyclization using bis(tributyltin).
Hill; White, American Chemical Journal, 1902, vol. 27, p. 196