Intramolecular Dehydro Diels−Alder Reactions of Diarylacetylenes:  Switching between Benzo[b]- and Benzo[c]fluorenones as Products by Controlling the Rearrangement of Cyclic Allene Intermediates

Abstract

Thermal cyclization of 1-[2-(arylethynyl)phenyl]-3-trimethylsilylpropynones affords a mixture of benzo[b]fluorenones and benzo[c]fluorenones. The ratio of the two isomers can be efficiently varied between 100:0 and 0:100 by introducing substituents with appropriate electronic and steric properties on the aryl rings and using an appropriate solvent.

Diastereoselective Synthesis of Eight‐Membered‐Ring Allenes from Propargylic Epoxides and Aldehydes by Silylene Insertion into Carbon–Oxygen Bonds

“…[a] Yield of product isolated from reaction run on a preparative scale (1 mmol). (7), C3-C4 1.321(8), O1-Si1 1.648(4), O2-Si1 1.637(4); C2-C3-C4 164.0(6), O1-Si1-O2 116.7 (2). [38] .…”

“…[1] As a result, eight-membered-ring allenes are either reactive intermediates [2,3] or require bulky substituents to stabilize them. Forcing the allene functionality into a medium-sized ring puts significant strain on the ring and distorts the allene from its optimal bond and torsional angles.…”

“…Forcing the allene functionality into a medium-sized ring puts significant strain on the ring and distorts the allene from its optimal bond and torsional angles. [1] As a result, eight-membered-ring allenes are either reactive intermediates [2,3] or require bulky substituents to stabilize them. [4,5] Introducing elements with longer atomic radii such as sulfur, selenium, phosphorus, or silicon reduces the ring strain of cyclic allenes sufficiently in some cases to permit isolation.…”

Diastereoselective Synthesis of Eight‐Membered‐Ring Allenes from Propargylic Epoxides and Aldehydes by Silylene Insertion into Carbon–Oxygen Bonds

“…Forcing the allene functionality into a medium‐sized ring puts significant strain on the ring and distorts the allene from its optimal bond and torsional angles 1. As a result, eight‐membered‐ring allenes are either reactive intermediates2, 3 or require bulky substituents to stabilize them 4. 5 Introducing elements with longer atomic radii such as sulfur, selenium, phosphorus, or silicon reduces the ring strain of cyclic allenes sufficiently in some cases to permit isolation 6–9.…”

Intramolecular Consecutive Dehydro‐Diels–Alder Reaction for the Catalytic and Enantioselective Construction of Axial Chirality

“…In particular,the intramolecular DDAreaction of aromatic enynes with alkynes has been used for the synthesis of multicyclic fused aromatic compounds,a nd both thermal and metal-catalyzed reactions have been reported (Scheme 2b). [11] Against this background, we envisioned that consecutive DDAr eactions of heteroatom-tethered aromatic enynes could be used in anew strategy for the enantioselective induction of axial chirality (Scheme 2c). [12] While afew examples of adiastereoselective DDA Scheme 1.…”