A Divergent Mcmurry Coupling of the Bis-Salisaldehyde with Methylene Linker: The Characterization of a Key by-Product with the Possible Pathway Formation

The McMurry coupling of a bis-salisaldehyde <b>3a</b> with methyl linker as the smallest members of its alkyl series is known to give the remarkably lower yield of the corresponding stilbenophanes. The half part of this molecule, unlike bigger analogues, is a good leaving group which afford<i>threo</i> isomer of 4H,4'H-4,4′-bibenzo[d][1,3]dioxine <b>4</b> in high diastereoisomeric ratio (99 &gt; ). A further study showed that the formation of this key by-product is the reason of the formation other by-products, namely 5a,10b-dihydrobenzofuro[2,3-b]benzofuran <b>9</b> and 2-(2,3-dihydrobenzofuran-2-yl)phenol <b>10</b>. Two reaction pathways for the formation of by-products have been proposed which are responsible for the unusual activity of dialdehyde <b>3a.</b>

以甲基为连接臂的双水杨醛（bis-salisaldehyde）<b>3a</b>，作为其烷基同系物中分子量最小的成员，经麦克默里偶联反应（McMurry coupling）后，对应生成的二苯乙烯型环番（stilbenophanes）产率显著偏低。该分子的半段结构与更大尺寸的同系物不同，属于优良的离去基团，可生成非对映异构体比例>99的4H,4'H-4,4′-联苯并[d][1,3]二氧六环<b>4</b>的苏式异构体（threo isomer）。进一步研究表明，该关键副产物的生成是其余副产物——即5a,10b-二氢苯并呋喃[2,3-b]苯并呋喃<b>9</b>与2-(2,3-二氢苯并呋喃-2-基)苯酚<b>10</b>——形成的原因。现已提出两条副产物生成的反应路径，可解释二醛<b>3a</b>的反常反应活性。