Carbon−Carbon Bond Formation from Small- and Medium-Ring Lactol Acetates via Radical and Oxonium Ion Intermediates. Synthesis of (±)-Laurenan

Divergent Diastereoselectivity in the Addition of Nucleophiles to Five-Membered-Ring Oxonium Ions

“…For example, reactions involving six-membered-ring electrophiles proceed with high stereoselectivity due to strong steric and stereoelectronic preferences . These effects can be seen in many examples of addition to cyclic iminium and oxonium ions. − Reactions involving the analogous five-membered-ring intermediates in some cases show high diastereoselectivity, but a general, predictive explanation for the origin of selectivity is lacking. − In studying reactions of oxasilacyclopentane oxonium ions 2 (Scheme ), we observed that the substitution pattern of the nucleophile determined the diastereoface that was attacked. Contrary to expectations, certain nucleophiles added with high diastereoselectivity to what appears to be the more hindered face.…”

A Convenient Approach towards the Synthesis of ADMDP Type Iminosugars and Nojirimycin Derivatives from Sugar-Derived Lactams

“…attributed to the high reactivity of the nucleophilic species involved [36]. The silyl cyanides require activation by a nucleophile in solution (such as the counterion of the Lewis acid) to form a pentacoordinate siliconate ion that transfers the cyano group.…”

“…The same modest diastereoselectivity was observed by Woerpel in the reaction of TMSCN with cyclic oxocarbenium ions [ 35 ]. Woerpel postulated that this effect can be attributed to the high reactivity of the nucleophilic species involved [ 36 ]. The silyl cyanides require activation by a nucleophile in solution (such as the counterion of the Lewis acid) to form a pentacoordinate siliconate ion that transfers the cyano group.…”

The reductive decyanation reaction: chemical methods and synthetic applications

“…The Li or Na/NH 3 system has been widely used in organic synthesis. [19][20][21][22][23][24][25][26][27] Rychnovsky investigated the alkylation and reductive decyanation of cyanohydrin acetonides such as 1 (Scheme 3). 28 The latter are key intermediates in the synthesis of polyene macrolide antibiotics such as roflamycoin, 29 17-deoxyroflamycoin 30 or filipin III.…”