Stadler Daniel, Bach Thorsten
Lehrstuhl für Organische Chemie I, Technische Universität München, 85747 Garching, Germany.
J Org Chem. 2009 Jul 3;74(13):4747-52. doi: 10.1021/jo900445c.
The 2-substituted 1-(2',2',3',3'-tetramethylcyclopropyl)-alkan-1-ols 3-7 were prepared by carbonyl addition of tetramethylcyclopropyl lithium to the respective aldehydes or by addition of the respective substituted carbanions to tetramethylcyclopropyl carbaldehyde 16. Under Brønsted acidic conditions (HBF(4).OEt(2)), the alcohols served as substrates in Friedel-Crafts alkylation reactions with 2-methylthiophene (8) and N-tosylpyrrole (9). The alkanols 3-6 carrying the groups (t)Bu, Ph, CN, PO(OEt)(2) in 2-position delivered the rearranged substitution products 17-20 in very good chemical yields (9 examples, 81-97%). The products were formed presumably via ring-opening of the tetramethylcyclopropyl-substituted cation, which rearrange by a Wagner-Meerwein shift to allylic cations I. The latter cations are eventually attacked by the arene nucleophile. The diastereoselectivity of this process is good (anti-preference for Ph, CN, PO(OEt)(2)) to excellent (syn-preference for (t)Bu). The esters 7, carrying a methoxycarbonyl group in 2-position, yielded under the same reaction conditions products 25 and 26, which are formed by an intermolecular Friedel-Crafts reaction followed by a subsequent intramolecular Friedel-Crafts alkylation (3 examples, 80-93%).
通过将四甲基环丙基锂羰基加成到相应的醛上，或通过将相应的取代碳负离子加成到四甲基环丙基甲醛16上，制备了2-取代的1-(2',2',3',3'-四甲基环丙基)-链烷-1-醇3-7。在布朗斯特酸性条件（HBF(4).OEt(2)）下，这些醇作为底物与2-甲基噻吩（8）和N-甲苯磺酰基吡咯（9）进行傅克烷基化反应。在2-位带有(t)Bu、Ph、CN、PO(OEt)(2)基团的链烷醇3-6以非常好的化学产率（9个例子，81-97%）得到重排的取代产物17-20。产物可能是通过四甲基环丙基取代的阳离子开环形成的，该阳离子通过瓦格纳-米尔温重排重排为烯丙基阳离子I。后者的阳离子最终被芳烃亲核试剂进攻。这个过程的非对映选择性良好（对Ph、CN、PO(OEt)(2)为反式偏好）到优异（对(t)Bu为顺式偏好）。在2-位带有甲氧基羰基的酯7在相同反应条件下得到产物25和26，它们是通过分子间傅克反应，随后进行分子内傅克烷基化形成的（3个例子，80-93%）。
