Synthesis of Angular Triquinanes from 1-Alkynylbicyclo[3.2.0]hept-2-en-7-ones. A Tandem Alkoxy-Cope Ring Expansion/Transannular Ring Closure Reaction

• Published in: Journal of organic chemistry Vol. 65; no. 25; pp. 8564 - 8573
• Main Authors: Verma, Sharad K, Fleischer, Everly B, Moore, Harold W
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 15.12.2000; Amer Chemical Soc
• Subjects: Bridged Bicyclo Compounds - chemical synthesis; Bridged Bicyclo Compounds - chemistry; Chemistry; Chemistry, Organic; Crystallography, X-Ray; Magnetic Resonance Spectroscopy; Mass Spectrometry; Molecular Structure; Physical Sciences; Science & Technology; REARRANGEMENT; SYSTEMS; STEREOCONTROLLED CONSTRUCTION; SQUARATE; POLYQUINANES
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo0009503

Addition of ethenyllithium reagents to the carbonyl group of dialkyl squarate-derived 1-alkynylbicyclo[3.2.0]hept-2-ene-7-ones (15), followed by a TBAF workup, results in a low-temperature anion-accelerated alkoxy-Cope rearrangement which proceeds by way of a strained cyclic allene intermediates (e.g.,17). This leads to the formation of angularly fused triquinanes (e.g., 20) in which each of the rings is functionally differentiated. Bicyclo[6.3.0]undecadienones (e.g., 36) are the major products when the reactions are quenched with aqueous bicarbonate rather than TBAF. Under analogous conditions 2-alkylidene-1-alkynylbicyclo[3.2.0]heptan-7-ones also give bicyclo[6.3.0]undecadienones by a mechanism that was established to involve a 1,5-hydrgen shift in a strained allene intermediate. The synthetic scope and mechanism of these and related transformations are discussed.