Site Selectivity of the Diels−Alder Reactions of 3-[1-(tert-Butyldimethylsilyloxy)vin-1-yl]furan and 3-(Propen-2-yl)furan. Synthesis of 4-Substituted Benzofurans

Abstract

The Diels−Alder reaction of 3-vinylfurans 5 and 27 with DMAD, N-phenylmaleimide, and dimethyl maleate afforded products derived both from addition to the furan ring diene system (intraannular addition) and to the furan 2,3-double bond 3-vinyl group diene system (extraannular addition). For example, compounds 6 and 7 were obtained from 5 and DMAD. In contrast, dienophiles containing a phenylsulfinyl group, such as 19−21, gave products derived exclusively from the extraannular reaction mode. These products are useful precursors of 4-substituted benzofurans, especially 4-hydroxybenzofurans.

Furanodendralenes

“…A small amount (4%) of the semicyclic diene addition product 9 was also isolated . This distribution of products is significantly different from all previous reports of cycloadditions involving more highly substituted 3-alkenylfurans. , It is also different to the computationally predicted selectivities of the reaction of 3-vinylfuran with maleic anhydride by Sastry . This result is, however, consistent with our M06-2X/6-311+G(2df,p)//B3LYP/6-31G(d) calculations, which predict a 1:1 ratio of endo : exo products and an 85:15 ratio of furan diene:semicyclic diene addition.…”

“…DTDA reaction sequences involving a furofuran and 3-alkenylfurans have been reported, as have single additions of dienophiles to the semicyclic diene site of 3-alkenylfurans . All prior work in this area involves furano[3]dendralenes, with two reports of DTDA reaction sequences previously published.…”

“…All prior work in this area involves furano[3]dendralenes, with two reports of DTDA reaction sequences previously published. Thus, Eberbach and co-workers reported a single example of a DTDA sequence involving a furofuran (Scheme a) and Benı́tez and co-workers examined the DTDA reactivity of substituted 3-alkenyl furans (Scheme b) . Two separate reports of single cycloadditions of dienophiles to the semicyclic diene site of 3-alkenyl furans have also appeared, in reactions that represent key steps in total syntheses of natural products (Scheme c,d) .…”

Chiral Holmium Complex-Catalyzed Diels–Alder Reaction of Silyloxyvinylindoles: Stereoselective Synthesis of Hydrocarbazoles

“…Ordinary transformation of the cycloadduct provides hydrocarbazolone 3 with a quaternary carbon. To our surprise, there is no synthetically useful example of the use of siloxy vinyl-substituted heteroaromatics as a diene for catalytic and enantioselective [4 + 2] cycloaddition . We report here a method for the catalytic synthesis of optically active hydrocarbazoles using siloxy vinylindole as a diene, in which new holmium (Ho) salt and chiral bis-thiourea complexes were used as a catalyst.…”

A facile access to highly functionalized triphenylphosphoranylidene succinimides through a three-component reaction and DFT investigation of the reaction mechanism

“…This molecule is highly electrophilic, and is widely employed as a dienophile in cycloaddition reactions, such as the Diels-Alder reaction. 21,22 Under the present reaction conditions and according to theoretical calculations, there is a possibility for competition between 4 and 5 for the initiation step of the reaction. The corresponding parameter which can differentiates between 4 and 5, is their electrophilic character.…”