Synthesis of 1,2,3,4‐Tetrahydro‐1,2‐dimethylidenenaphthalene: A Reactive s‐cis‐Butadiene Undergoing Highly Chemo‐ and Regioselective Cyclodimerization |
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Authors: | Elena Roversi Pierre Vogel Kurt Schenk |
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Abstract: | 1,2,3,4‐Tetrahydro‐1,2‐dimethylidenenaphthalene 11 has been derived in three steps from tetralone. In the condensed state and at −80°, it undergoes a highly chemo‐ and regioselective cyclodimerization to give 3,3′,4,4′‐tetrahydro‐2‐methylidenespironaphthalene‐1(2H),2′(1′H)‐phenanthrene] ( 14 ), the structure of which has been established by single‐crystal X‐ray‐diffraction analysis. Dimer 14 undergoes cycloreversion to diene 11 under flash‐pyrolysis conditions. The reaction of diene 11 with SO2 occurs without acid promoter at −80° and gives a mixture of (±)‐1,4,5,6‐tetrahydronaphth1,2‐d]1,2]oxathiin 2‐oxide ( 23 ; a single sultine), 1,3,4,5‐tetrahydronaphtho1,2‐c]thiophene 2,2‐dioxide ( 25 ), and dimer 14 . The high reactivity of diene 1 in its Diels‐Alder cyclodimerization and its highly regioselective hetero‐Diels‐Alder addition with SO2 can be interpreted in terms of the formation of relatively stable diradical intermediates or by concerted processes with transition states that can be represented as diradicaloids. |
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