Green and Rapid Access to Benzocoumarins via Direct Benzene Construction through Base‐Mediated Formal [4+2] Reaction and Air Oxidation

Abstract

Benzocoumarini sa ni mportant structural motif widely found in natural productsa nd synthetic molecules.T raditional methods for the synthesis of benzocoumarins and theird erivatives require multiple steps,t ypically with an intramolecular ester forming reactiont om ake the lactone ring as the last step. Anothermajor method involvestransition metal-catalyzed coupling or carbon-hydrogen bond activation reactions starting with pre-existing aryl frameworks in the substrates.H ere we report an ew strategy for the greena nd rapid access to benzocoumarins and their derivatives.O ur method uses readilya vailableu nsaturated aldehydes and coumarins as the substratesa nd air as the green oxidant. Theo verallr eactionp roceeds through af ormal [4+ +2] process to construct an ew benzene ring andt hust oa fford benzocoumarins in essentially as ingle step.N om etal catalysts were used;n o toxic or expensive reagents were involved. The power of our new approach is further demonstrated in ac oncise formal total synthesis of cannabinol, abioactive natural product.

Synthetic Approaches to Mono- and Bicyclic Perortho-Esters with a Central 1,2,4-Trioxane Ring as the Privileged Lead Structure in Antimalarial and Antitumor-Active Peroxides and Clarification of the Peroxide Relevance

“…(E)-3-(4-Methoxyphenyl)but-2-enal ( 4b ) [ 51 ]. Following GP-3, 1.79 g (10.1 mmol) of the alcohol 4a and 18 g of MnO 2 in 250 mL of toluene were reacted.…”

Synthesis of 6H-Benzo[c]chromenes via Palladium-Catalyzed Intramolecular Dehydrogenative Coupling of Two Aryl C–H Bonds

“…14 More recently, Chi et al developed a base-mediated [4 + 2] reaction to construct the benzene ring and with it as the key step finished the total synthesis of cannabinol. 15 Our synthesis of cannabinol started from compound 4, which could be obtained from commercially available 5-pentyl-1,3-diphenol through two steps in 78% overall yield (for details, see the Supporting Information). Then, under our optimized conditions, intramolecular two aryl C−H/C−H coupling cyclization of 4 smoothly gave the 6H-benzo [c]chromene 5 in 85% yield (Scheme 6).…”

Total Synthesis of Pulchrol and Pulchral

“…pulchrol 和 pulchral 的合成路线如 Scheme 3 所示. [12,13] , 产率 80%. 化合物 13 与甲基锂经过亲核取 代, 在酸性条件下关环且脱保护得到化合物 1, 两步产 率 60%, 将化合物 1 氧化得到 2, 产率 80%.…”