Decorated Cyclopentadienes from Acetylene and Ketones in Just Two Steps

Abstract

The products of the one-pot assembly of acetylene and ketones in the KOH/DMSO system, 7-methylene-6,8-dioxabicyclo[3.2.1]octanes, undergo an acid-catalyzed (CFCOOH, room temperature) rearrangement to rarely substituted cyclopentadienes in good-to-excellent yields. The mechanism of the rearrangement has been supported by the isolation and corresponding transformations of two intermediates.

Functionalized Thieno[3,2‐b]pyrroles from Acylthiophenes, Acetylene Gas and Hydrazines in Two Steps

“…Further increase in temperature up to 60°C did not augment the yield of 3 fa, the formation of the cyclopentadiene 4 f (95 % yield), the product of acid-catalyzed rearrangement of DOBCO 1 f, being observed (Scheme 5). [20] Next, the scope of hydrazines 2 was examined for the transformation under the similar conditions (Scheme 6). For each pair DOBCO 1/hydrazine 2, optimal conditions were found that ensured the maximum yield of thieno[3,2-b]pyrroles 3 and full conversion of the starting compounds.…”

Synthetic Routes towards Multifunctional Cyclopentadienes

“…Starting from simple ketones and acetylenes, 7‐methylene‐6,8‐dioxa‐bicyclo[3.2.1]octanes were obtained and rearranged to the final Cps under acidic conditions and at ambient temperatures (Scheme D). A tentative 11‐step mechanism involving the formation of a carbocation species, which promotes the intramolecular ring closure, was supported by the isolation and characterization of two key intermediates …”

“…At entative 11-step mechanism involving the formationo facarbocation species, which promotes the intramolecular ring closure, was supported by the isolation and characterization of two keyi ntermediates. [68]…”

Acetylene in Organic Synthesis: Recent Progress and New Uses

“…As an alternative to Favorskii reaction, ketones and acetylene can undergo a one-pot cascade cyclization to give 7-methylene-6,8-dioxabicyclo[3.2.1]octanes [ 145 , 146 , 147 , 148 , 149 , 150 ]. Under optimized conditions [ 145 , 146 ] a variety of bicyclic products were obtained from dialkyl [ 145 ] and aryl alkyl [ 146 , 147 ] ketones ( Scheme 60 ).…”