Ambient Synthesis of Tricyclic Naphthalenes via Stepwise Styryl-yne Dearomative Diels–Alder Cyclization

Abstract

A cascade of styrylynols promoted by MnO2 allows the synthesis of fused tricycles with a naphthalene core. The reaction occurs under ambient conditions, offering a practical synthetic tool because of the inexpensive and abundant manganese species. The method affords products through the sequential oxidation of a propargyl alcohol, stepwise Diels–Alder cyclization, and finally rearomatization. According to density functional theory, the usually unfavorable stepwise Diels–Alder mechanism is instead a general tool for eliciting otherwise challenging dearomative annulation.

Diastereoselective synthesis of tetrahydropyranes via Ag(i)-initiated dimerization of cinnamyl ethers

“…The method involves a sequential C(sp 3 )-O bond cleavage/C(sp 3 )-H bond functionalization, which is an original reactivity in the field of Ag-promoted processes. [17][18][19][20] As part of an ongoing interest on synthetic cascades, [21][22][23][24][25] we serendipitously observed the formation of macrocycle 2 in the presence of a Ru-based catalytic system originally developed by Sato and Mori 26 while treating diendiyne 1 with an Ag (I) salt. We soon realized that the Ag(I) salt used to trigger a putative chloride abstraction was actually the competent species for the conversion of 1 into 2.…”

“…As part of an ongoing interest on synthetic cascades, 21–25 we serendipitously observed the formation of macrocycle 2 in the presence of a Ru-based catalytic system originally developed by Sato and Mori 26 while treating diendiyne 1 with an Ag( i ) salt. We soon realized that the Ag( i ) salt used to trigger a putative chloride abstraction was actually the competent species for the conversion of 1 into 2 .…”

“…In order to test these hypotheses, 30 DFT modelling studies were carried out at the M06/Def2-svp level, using DCM as implicit solvent. 22,23 The reaction was tested on substrate 3c.…”

Sequential Strategies to Trigger Mild Dearomative Diels–Alder Cyclizations

“…As part of an ongoing interest in atom-economical cascades, − we recently reported a MnO 2 -promoted sequence that converts styrylynols into tricyclic naphthalenes . Substrates were prepared by treating a 1,6-enyne with butyl lithium and quenching the so-formed carbanion with an acyl chloride.…”

“…The sequence leading to 5 is the first example of a dearomative Diels–Alder cyclization using electronically unbiased partners. − ,− ,, Applications are at present limited to the use of extended aromatics, for which the intermediate dearomatization has a lower energetic cost compared to that of phenyl groups (such as those of enynes 1 ) because of the energy mismatch in the frontier orbitals involved in the cycloaddition.…”