Gharpure Santosh J, Nanda Santosh K, Shelke Yogesh G
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India.
Chemistry. 2017 Jul 26;23(42):10007-10012. doi: 10.1002/chem.201701659. Epub 2017 Jul 5.
A transition metal free, acid promoted cascade hydroalkoxylation-formal [4+2] cycloaddition of various alkynols with salicylaldehyde is demonstrated for the synthesis of tetrahydrofurano/pyrano-chromenes and spiroketals. In general, alkynols underwent hydroalkoxylations in an endo-dig manner when internal alkynes were used to furnish the heteroannular ketals, whereas terminal alkynes proceeded in an exo-dig fashion leading to spiroketals. The study revealed that intramolecular hydroalkoxylation of alkynols is a preferred path over a generation of oxonium ions when coupling partner is salicylaldehyde. This metal-free transformation provides a new avenue for the stereoselective synthesis of tetrahydrofurano- and pyrano-chromenes in an expeditious manner.
展示了一种无过渡金属、酸促进的各种炔醇与水杨醛的级联氢烷氧基化-形式上的[4+2]环加成反应，用于合成四氢呋喃并/吡喃并色烯和螺缩酮。一般来说，当使用内炔来提供杂环缩酮时，炔醇以内型亲核加成的方式进行氢烷氧基化反应，而末端炔则以外型亲核加成的方式进行反应，生成螺缩酮。研究表明，当偶联伙伴是水杨醛时，炔醇的分子内氢烷氧基化反应比生成氧鎓离子是更优先的途径。这种无金属转化为快速立体选择性合成四氢呋喃并和吡喃并色烯提供了一条新途径。
