Science of Synthesis

Salaün, J., Science of Synthesis, (2005) 26, 565.

Although the most common nonphotolytic route to four-membered carbon rings is that of [2+2] cycloaddition of ketenes to alkenes, the parent ketene and simple alkylketenes are inert toward nonactivated or electron-deficient alkenes. Therefore, this method is limited to specific classes of alkenes, namely electron-rich and activated alkenes. Moreover, the reaction has the disadvantage of competing dimerization and oligomerization of the starting ketenes. Nevertheless, the [2+2] cycloadducts of arylketenes and cyclopentadiene can be obtained in good yields. For example, dehydrohalogenation of 2-phenylpropanoyl chloride by triethylamine gives 2-methyl-2-phenylketene, which reacts very smoothly with cyclopentadiene to give the endo-cycloadduct ‌37‌ in 85% yield as a single diastereomer (‌Scheme 15‌).[‌41‌]

‌Meeeee 88‌ [8+8] Meeeeeeeeeeee ee e Meeeee ee Meeeeeeeeeeeeee[‌88‌]

8-Meeeeeeeeeeeee-8-eeeeee ‌88‌ (M8 = M, Me), eeeeee ee [8+8] eeeeeeeeeeeee ee eeeeee ee eeeeeeeeeeeeeee (M8 = M) ee 8-eeeeeeeeeeeee (M8 = Me) ee 88 eee 88% eeeeee, eeeeeeeeeeee, eeeee eeee eeeeeeeeeeeee ee eeeeeeeeeeee ee eeee eee 8,8-eeeeeeeeeeeee eeeeeeee-8-eeeeee ‌88‌ (M8 = M, Me; M8 = Me, Me) ee 88–88% eeeeee (‌Meeeee 88‌).[‌88‌] Meee eeeeeee ee eeeeeee eeeeeeeee ee eeeeeeee-8-eeeeee ‌88‌ eee eeeeee ee Meeee eeeee eeeeee eeee eeeeeeee Meeeee eeee, eeeeeeeeeeeee eeeeeee ee eee eeee eeeeee, eee eeee-8,8-eeee-8-eeee ‌88‌ eee eeeeee. Meeeeeeeee [8+8] eeeeeeeeeeeee ee eeee-8,8-eeee-8-eeee ‌88‌ eeee eeeeeeeee-8,8-eeeee eeeeeeee 8-eeeeeeeeeeee[8.8.8]eee-8-ee-8-eeee ‌88‌, eeeee ee eeeeeee eeeeeee (888°M eee 8 e) eee eeeeeeeeee eeee eeeeeee[8.8.8]eeee-8,8-eeee-8-eeee ‌88‌ (eeeeeee eeeee eeee ‌88‌: 88–88%), eeeeee ee eeeee-eeeeeeee-eeee eeeeeeeeee (‌Meeeee 88‌).[‌88‌] Meeeeeeeeeeee, eeeeeeeeeeeee-eeeeeeee 8,8-eeeeeeeeeeeeeeeeeee ee α,β-eeeeeeeeeee eeee eeeeeeeee eeee eeeeee eee eeeeeeeeee ee eeee-8,8-eeee-8-eeee ‌88‌ eee eee eeeeeeeee ee eee eeeeeeeeeeee 8-eeeeeee­eeeee[8.8.8]eee-8-ee-8-eeee ‌88‌.[‌88‌]

‌Meeeee 88‌ Meeeeeeeeee ee Meeeeeee 8-Meeeeeeeeeeeeeeeeee ee eee Meeeeeeeeee ee Meeeeeee-8-eeeeee[‌88‌]

Meeeeeeeeeeeee eeeeee ee eeeeee eeeeeeeeeeeee eee eeee eeeeeeee eeeeeeeeeee.[‌88‌] Mee eeeeeeeeee ee eee eeeeeeee eeeeeee ee eee eeeeee eee eeeeeeee ee eee eeeeee eeeeee: eeeee-eeee eeeeeee eeeeeee eee eeeeee eee eeeeee eeeeeeee eeee eee eeee eeeeee. Mee eeeeeeee eeeeeeeeeeeeee eeeeeee ee eee eeeeeeeeeeee ee eee eeeeee eeeeeeee, eeeee eeeeeeeee eeeeeeeeeeeee eeee eeeeeeeee ee eeeeeeeeeeeee. Mee eeeeeeeeee ee eeeeeee ee eeeeeeeeeeeeee eeeeeeeeeeeeee ee eeeeeee ee eeee ee eeeeeeeeeeeeee eeeeeeeee eeeeeeeee eeeeeeeee eeeeee-, eeeee-, eee eeeeeeeeeeeee. Meee eeeee eeeeeeeee ee eeeeeee eeeeeeee eeee eeee eeeee ee eeeeeee eeeeeeeeeeeeee eeeeee–eeeeee eeeeeeeeeeeeee.[‌88‌–‌88‌] Me eeeeeee ee eee eeeee eeeeeeeee ee eeeeeeeee eee eeeeeeeeeeeee ‌88‌, eeeeee ee 88% eeeee eeee eeee eeeeeeee ‌88‌ ee eeeeeeeeeeeeeeeeee (‌Meeeee 88‌).[‌88‌]

‌Meeeee 88‌ Meeeeeeeeee ee e Meeeeeeeee Meeeeeeeeeeee ee ee Meeeeeeeeeeeee Meeeee–Meeeee Meeeeeeeeeeee ee eee Meeee Meeeeeeee ee Meeeeeeee[‌88‌]

Meeeeee[8.8.8] eeee eeeeeee eee ee eeeeeeee ee eeeeeeeeeeeeee eeeeee–eeeeee eeeeeeeeeeeeee.[‌88‌] Meee, eeeeeeeeee ee eee eeeeeee eeeeeeeee 8,8-eeeeeeeeeeeeeeeee-8-eee-8,8-eeeee (‌88‌) ee eeeeeee Meeeeeee eeeeeeee, eeeeeeee ee M-eeeeeeeeee eeeee 8-eeeee-eeeeeeeeeee eeeeeeee-8-eeeeee ‌88‌ (‌Meeeee 88‌).[‌88‌] Meeeeeeeeee ee eeeeeeee-8-eeeeee ‌88‌ ee eeeeeee ee e eeeeee eeee ee 888°M eeeee, eee eeeeeeeeeeee ‌88‌, ee eeeeeee[8.8.8]eeee-8-ee-8-eeee ‌88‌.

‌Meeeee 88‌ Meeeeeeeeee ee Meeeeee[8.8.8]eeeeeeeeee eee Meeeeeeeeeee ee Meeeeeeeeeeeee Meeeee–Meeeee Meeeeeeeeeeeee[‌88‌]

Meeeeeeeeeee Meeeeeeee

(8M*,8M*,8M*)-8-Meeeee-8-eeeeeeeeeeeee[8.8.8]eeee-8-ee-8-eee (eeee-‌88‌); Meeeeee Meeeeeeee:[‌88‌]

M eeee ee Me8M (88 e, 8.8 eee) ee eeeee eeeeee (88 eM) eee eeeee eeeeeeee eee eeee eeeeeeee ee ee ee e eeee ee 8-eeeeeeeeeeeeeee eeeeeeee (88.8 e, 8.8 eee) ee eeeee eeeeee (888 eM) eeeeeeeeee eeeeeee eeeeeeeee eeeeeeeeeeeeeee (88 e, 8 eee). Meeee 8 e ee eeeeeeee, eee eeeeeee eee eeeeeeee eeeee eee eeeeee eeeee ee eee eeeeee eeeeeeeeeee (8–88 e). Mee Me8M•MMe eeee eee eeeeeee ee eeeeeeeeee, eee eeeeeeee eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee, eee eeeee eeeeeee eee eeeeeeeeeeeeee (Me8M); eeeee: 88.8 e (88%); ee 88–88°M.

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) 8/8, 888.
• 8.Meeeee-Meee, (8888) 8/8, 888.
• 8.Meeeee-Meee, (8888) 8/8, 888.
• 8.Meeeee-Meee, (8888) 8/8, 888.
• 8.Meeeee-Meee, (8888) 8/8, 888.
• 8.Meeeee-Meee, (8888) 8/8, 888.
• 8.Meeeee-Meee, (8888) 8/8, 888.
• 8.Meeeee-Meee, (8888) 8/8, 888.
• 8.Meeeee-Meee, (8888) 8/8e, 8888.
• 8.Meeeee-Meee, (8888) M 88e8, 8888.
• 8.Meeeee-Meee, (8888) M 88e8, 8888.
• 8.Meeeee-Meee, (8888) M 88-8, 8888.
• 8.Meeeee-Meee, (8888) M 88-8, 8888.
• 8.Meeeee-Meee, (8888) M 88-8, 8888.
• 8.Meeeee-Meee, (8888) M 88-8, 8888.
• 8.Meeeee-Meee, (8888) M 88-8, 8888.
• 8.Meeeee-Meee, (8888) M 88-8, 8888.
• 8.Meeeee-Meee, (8888) M 88-8, 8888.
• 8.Meeeee-Meee, (8888) M 88-8, 8888.
• 8.Meeeee-Meee, (8888) M 88e, 8888.
• 8.Meeeee-Meee, (8888) M 88e, 8888.
• 8.Meeeee-Meee, (8888) M 88e, 888.
• 8.Meeeee-Meee, (8888) M 88e, 8888.
• 8.Meeeee-Meee, (8888) M 88e, 888.