By using o-benzoquinone as an internal oxidant, the regio- and diastereoselective functionalization of the secondary over the tertiary α-C-H bond of 2-substituted pyrrolidines is first realized. Subsequent intermolecular addition of a nucleophile to the generated N,O-acetal and cleavage of the aromatic substituent leads to 2,5-disubstituted pyrrolidines.
A redox-neutral α-C-H oxygenation of commercially available pyrrolidin-3-ol with a monoprotected p-quinone generated an N-aryliminium ion intermediate, which reacted in situ with boronic acid nucleophiles to produce a series of cis-2-substituted pyrrolidin-3-ols. With this strategy, 8-epi-(-)-lentiginosine was synthesized from (3R,4R)-pyrrolidine-3,4-diol in three steps.
In refluxing 9 : 1 (v/v) H2O-1,4-dioxane and without an additional catalyst, the rearrangements of various types of cyclopropyl carbinols were attempted. It was found that the reactions generally gave homoallylic alcohols in good to very high chemical yields. Rearrangements of bicyclic or tricyclic cyclopropyl carbinols readily gave the desired ring-expanded cyclic homoallylic alcohols which are difficult to synthesize by other means.
A divergent approach to generate either 1-hydroxymethylindenes (which could then be converted to benzofulvenes through a dehydration reaction) or naphthalenes by the rearrangement of cycloprop[2,3]inden-1-ols is reported. The effect of the cyclopropyl ring substitution pattern on ringopening/expansion rearrangements of the substrates was systemically studied.
The reaction of o‐quinone (I) with pyrrolidine (II) gives the polycyclic N,O‐acetal (III) which can be readily converted to disubstituted pyrrolidines (V) and (VIII).
The rearrangement of various types of cyclopropyl carbinols in refluxing H2O/dioxane mixtures without any additional catalyst gives generally homoallylic alcohols.
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