261352-97-0Relevant academic research and scientific papers
Stereochemistry of addition of organometallic reagents to 2-acyloxanes and 2-acylthianes
Alvarez-Wright, Maria Teresa,Satici, Hikmet,Eliel, Ernest L.,White, Peter S.
, p. 617 - 629 (2007/10/03)
The stereochemistry of addition of a number of organometallic reagents, including methyllithium, methyllithium-YbCl3, 1-pentynyllithium, and 1-pentynyllithium-YbCl3 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-YbCl3 to conformationally locked 1,3-oxathianes; however, addition of methyllithium-YbCl3 to all 1,3-oxathianes studied and of pentynyllithium-YbCl3 to the conformationally mobile 2-benzoyl-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.YbCl3 (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-YbCl3 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.
