0 Hits

  • Previous / Next

You are using Science Of Synthesis as a Guest.
Please login or sign up for a free trial to access the full content. Method 2: High-Pressure Diels–Alder Cyclizations of Furans and Activated Alkenes

DOI: 10.1055/sos-SD-037-00286

Ding, K.; Wang, Z.Science of Synthesis, (200837521.

Under ambient conditions, the cycloadditions between furans and less activated alkenes often take place slowly and with very poor to mediocre yields. High reaction temperatures cannot be used to accelerate these sluggish reactions because cycloaddition products derived from furan are generally susceptible to thermal cycloreversion to the starting materials. The use of high pressure, on the other hand, is a valuable technique to promote these reactions that have large negative activation volumes. Typically, a compressible sample tube containing a dichloromethane solution of furan and a dienophile is kept under hydrostatic pressure (1.5 GPa) at room temperature in a hydraulic press for a specified period of time. Good yields of cycloadducts 149 can be obtained using otherwise inert dienophiles (Scheme 63). For the reaction of acrylic dienophiles with furan, the use of high pressure generally affords the cycloadduct in higher yield within a shorter reaction time as compared to normal thermal conditions. Moderate yields are also realized in the reaction of propenal or methyl vinyl ketone with furan to give products 149 (R1=R2=H; R3=Ac, CO2Me) (Scheme 63). However, the crotonic or methacrylic dienophiles only give poor yields of cycloadducts 149 (R1 or R2=Me, respectively), presumably owing to the steric hindrance and electronic deactivation induced by the methyl groups. For dienophiles with two ester groups, excellent yields of cycloadducts 149 (R1=H; R2=R3=Ac, CO2Me) are obtained. For each case of the high-pressure reaction, approximately 1:1 ratios of exo/endo isomers are produced. A limitation to this procedure is that the 1.5 GPa apparatus is not commonly accessible in many laboratories. Although the general procedure for this high-pressure process is known, the detailed workup of the cycloadducts is not reported.[‌94‌]

Meeeee 88 Meee-Meeeeeee MeeeeMeeee Meeeeeeeeeee ee Meeee eee Meeeeeeee Meeeeeeeeee[‌88‌‌88‌]

Meeeeeeeeee 88

M8 M8 M8 Meeeeeeeee Meeee (%) Mee
M M MM 8.8MMe, ee, 8 eeeee 88 [‌88‌]
M M MM MM8Me8, 8.8 MMe, ee, 8e 88 [‌88‌]
M M MM8Me 8.8MMe, 88°M, 8 eeeee 88 [‌88‌]
M M MM8Me MM8Me8, 8.8 MMe, ee, 8e 88 [‌88‌]
Me M MM 8.8MMe, ee, 8 eeeee 88 [‌88‌]
Me M MM MM8Me8, 8.8 MMe, 88°M, 8e 88 [‌88‌]
MMe M MM eeeeee eeee, 88°M, 88e 88 [‌88‌]
MMe M MM MM8Me8, 8.8 MMe, 88°M, 88e 88 [‌88‌]
M M MMM MM8Me8, 8.8 MMe, ee, 8e 88 [‌88‌]
M M Me MM8Me8, 8.8 MMe, ee, 8e 88 [‌88‌]
M Me MM8Me MM8Me8, 8.8 MMe, ee, 88e 8 [‌88‌]
M Me MMM MM8Me8, 8.8 MMe, ee, 8e 88 [‌88‌]
M Me Me MM8Me8, 8.8 MMe, ee, 8e 88 [‌88‌]
M Me MM MM8Me8, 8.8 MMe, ee, 88e 8 [‌88‌]
Me M MMM MM8Me8, 8.8 MMe, ee, 8e 8 [‌88‌]
Me M MM8Me MM8Me8, 8.8 MMe, ee, 8e 8 [‌88‌]
M MM8Me MM8Me MM8Me8, 8.8 MMe, ee, 8e 88 [‌88‌]
M MM8Me MM8Me MM8Me8, 8.8 MMe, ee, 8e 88 [‌88‌]

Meeeeee eeee-eeeeeeee MeeeeMeeee eeeeeeeeeeeeee eeee eeee eeee eeeeeeee eee 8-eeeeeeeeeee ee 8,8-eeeeeeeeeeeee eeee eeeeeeeeeeeee eeeeee eeeeeeeeeee (Meeeeee 88[‌888‌] eee 88[‌88‌]). Mee eeeeeeeee eee eeeeeee eee ee eeeeeeeeeeeeeee ee eeee eeeeeeeeeee eeeee e eeeeeeeeeee eeeeeeee ee 8.88.8 MMe eeee eeeeee eeeeeeeee eeeeeeeee, eeeeeee ee eeee ee eeeeeeeee eeeeee ee eeeeeee 8-eeeeeeeeee[8.8.8]eeee-8-eee eeeeeeeeeee eeee eee ee eee eeeeee eeeeeeeeeee(e) ee eee eeeeeeeeee eeeeee(e) (e.e., 888 eee 888).

Meeeee 88 Meee-Meeeeeee MeeeeMeeee Meeeeeeeeeeeee ee 8-Meeeeeeeeee eee Meeeeeeeeeeee Meeeeeeeeee[‌888‌]

Meeeeeeeeee 88

M8 M8 Meeee (eeee/eee) Meeee (%) Mee
M MM 88:88 888 [‌888‌]
M MM8Me 88:88 888 [‌888‌]
M MMM 888 [‌888‌]
Me MM8Me 88 [‌888‌]
Me MMM 88:88 88 [‌888‌]

Meeeee 88 Meee-Meeeeeee MeeeeMeeee Meeeeeeeeeeeee ee 8,8-Meeeeeeeeeeee eee Meeeeeeeeeeee Meeeeeeeeee[‌88‌]

Meeeeeeeeeee Meeeeeeee

8-Meeeeeeeee[8.8.8]eeee-8-eee Meeeeeeeeee 888 eee 888; Meeeeee Meeeeeeee:[‌88‌,‌888‌]

Mee eeeeeeeee eeee eeeeeeeee ee e eeeeeeeee eeeee eeee M-eeee eee eeeee-eeee eeeee eeeee eeeeeeee ee eee eeeeeeee eeeeeeeeeee. M MM8Me8 eeee ee eeeeeeeee eeeeeeeeee ee eee eeeeeeeee eee eeeeee ee e eeeeeeeeeeee Me/Me eeeeeeee eeee eee eeee eeeee eeeeeeeeeee eeeeeeee (8.8 MMe) ee ee eee eee eeeee eeeeeeeee. Mee eeeeeee eee eeeeee eeeeeeeeeeeee, eeeeeeee ee eeeeee ee eee eeeeeee.