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首页> 外文期刊>Journal of the Indian Chemical Society >Stereochemistry of addition of organometallic reagents to 2-acyloxanes and 2-acylthianes
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Stereochemistry of addition of organometallic reagents to 2-acyloxanes and 2-acylthianes

机译：将有机金属试剂添加到2-酰基氧烷和2-酰基噻吩的立体化学

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摘要

The stereochemistry of addition of a number of organometallic reagents, including methyllithium, methyllithium-YbCl_3, 1-pentynyllithium, and 1-pentynyllithium-YbCl_3 to 2-acyloxanes, 2-benzoylthianes, several substituted 1,3-oxathianes and 2-methoxyacetylthiane has been studied. For the ring systems containing oxygen atoms, almost all of the additions proceed in accordance with Cram's chelate rule, on the assumption that the chelation takes place with the oxygen rather than the sulfur atoms of the ring where both are present. An exception (cf. Utimoto et al.~7) is the addition of 1-pentynyllithium-YbCl_3 to conformationally locked 1, 3-oxathianes; however, addition of methyllithium-YbCl_3 to all 1, 3-oxathianes studied and of pentynyllithium-YbCl_3 to the conformationally mobile 2-benzoly-1, 3-oxathiane proceeds 'normally'. Additions to 2-benzoylthiane are usually of low stereoselectivity and often proceed contrary to what would be predicted on the assumption that the organometallic reagent chelates with sulfur; an exception is methylmagnesium iodide which does follow Cram's chelate rule. The additions of RLi and RLi.YbCl_3 (R methyl or 1-pentynyl) to 2-benzoylthiane follow the same stereochemical course presumably proceeding contrary to Cram's chelate rule; thus the reversal observed with 1-pentynyllithium-YbCl_3 in the 1, 3-oxathiane series appears not to be due to chelation with sulfur. The results with 2-methoxyacetylthiane suggest that chelation with the side-chain oxygen substituent prevails over chelation with the ring sulfur atom.
机译：已经向2-酰基氧烷，2-苯甲酰基噻吩，几种取代的1,3-氧杂蒽和2-甲氧基乙酰基噻吩中添加了多种有机金属试剂，包括甲基锂，甲基锂-YbCl_3、1-戊炔基锂和1-戊炔基锂-YbCl_3的立体化学。研究。对于含有氧原子的环系统，几乎所有的加成都按照克拉姆的螯合规则进行，假定螯合是与氧而不是环中同时存在的硫原子发生的。一个例外（参见Utimoto et al。〜7）是在构象锁定的1，3-氧杂蒽上加了1-戊炔基锂-YbCl_3。然而，将甲基锂-YbCl_3添加到所研究的所有1，3-氧杂蒽中，并将戊炔基锂-YbCl_3添加到构象可移动的2-苯甲酰基-1，3-氧杂蒽中，“通常”进行。 2-苯甲酰基噻吩的加成通常具有低的立体选择性，并且通常与假定有机金属试剂与硫螯合的假设相反地进行。甲基碘化镁例外，它确实遵循克拉姆的螯合规则。将RLi和RLi.YbCl_3（R甲基或1-戊炔基）添加到2-苯甲酰基噻吩中遵循相同的立体化学过程，大概是与克拉姆的螯合规则相反的。因此，在1、3-氧杂蒽系列中用1-戊炔基锂-YbCl_3观察到的逆转似乎不是由于与硫的螯合。用2-甲氧基乙酰基噻吩的结果表明，与侧链氧取代基的螯合作用优于与环硫原子的螯合作用。

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