Synthesis of Linear and Angular Triquinane Skeletons by O-Stannyl Ketyl-Promoted Fragmentation−Cyclization Reactions of α-Keto Cyclopropanes

Abstract

Several investigations of rigid alpha-keto cyclopropane cleavage by O-stannyl ketyls are summarized herein. Tricyclo[3.3.0.0(2,8)]octan-3-one ring systems were treated with nBu(3)SnH, which produced different ring-cleavage products depending on the location and type of substituent present. An examination of both radical-stabilizing substituents and stereoelectronic factors was initiated to understand what factors bias bond cleavage in a configurationally restricted alpha-ketocyclopropane via O-stannyl ketyls. A preference for cleavage of the cyclopropane bond with the best orbital overlap with the ketyl radical sp(2)-orbital even in the presence of radical stabilizing groups is indicated by these results. An O-stannyl ketyl ring scission-cyclization resulted in the novel synthesis of either a linear or an angular triquinane skeleton depending on the length and location an alkene tether on the tricyclo[3.3.0.0(2,8)]octan-3-one precursor.

Programming Organic Molecules: Design and Management of Organic Syntheses through Free-Radical Cascade Processes

“…In both this, and the ketyl radical study, an FCC cascade was also described. Enholm and Jia put this type of FC cascade to good use in tin hydride mediated preparations of linear and angular triquinanes, which were obtained in excellent yields 104…”

Photochemistry of Tricyclo[5.2.2.02,6]undeca‐4,10‐dien‐8‐ones: An Efficient General Route to Substituted Linear Triquinanes from 2‐Methoxyphenols. Total Synthesis of (±)‐Δ9(12)‐Capnellene

“…Enholm and Jia developed a radical-mediated method [30] for the cleavage of analogous compounds. Thus, treatment of compounds 12 with nBu 3 SnH and azobisisobutyronitrile (AIBN) in refluxing benzene provided the desired linear triquinanes 18 in good yields with cis/anti/cis stereostructures (Table 7).…”

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“…For this purpose, after considerable experimentation, the acetyl group was selectively protected under the conditions reported by Noyori and co‐workers10 to deliver monoacetal 8 in quantitative yield. Opening of the strained cyclopropane ring of 8 with tributyltin hydride/AIBN11 led to the quantitative formation of linear triquinane 9 . Ketone 9 was then transformed into enol triflate 10 by using 2‐pyridyltrifluoromethanesulfonimide 12.…”