Covalent Tethers for Precise Amino Alcohol Syntheses: Ring Opening of Epoxides by Pendant Sulfamates and Sulfamides

A Catalytic, Enantioselective Sulfamate Tethered Aza-Michael Cyclization

We show the first examples of enantioselective cyclization reactions of tethered sulfamates onto pendant α,β-unsaturated esters, ketones, and thioesters. This reaction is promoted by a new chiral bifunctional guanidine catalyst and is operationally very simple. A variety of primary sulfamates and sulfamides were examined, and in many cases, products were delivered in excellent yields and enantiomeric ratios. With secondary sulfamates, kinetic resolutions were possible. The product oxathiazinanes are very useful chiral synthons.

Exploration of One-Pot, Tandem Sulfamoylation and aza-Michael Cyclization Reactions for the Syntheses of Oxathiazinane Dioxide Heterocycles

We show the first examples of one-pot tandem sulfamoylation/aza-Michael reactions for the preparation of oxathiazinane dioxide heterocycles from linear alkenyl alcohol precursors. Our optimized protocols are tolerant of a variety of functional groups and provide products that are amenable for further transformations. The reactions scale well, and no special precautions are required to exclude air or ambient moisture.

Regio- and stereoselective access to highly substituted vinylphosphine oxides via metal-free electrophilic phosphonoiodination of alkynes

In general, the P-centered ring-opening of quaternary phosphirenium salts (QPrS) predominantly leads to hydrophosphorylated products, while the C-centered ring-opening is primarily confined to intramolecular nucleophilic reactions, resulting in the formation of phosphorus-containing cyclization products instead of difunctionalized products generated through intermolecular nucleophilic processes. Here, through the promotion of ring-opening of three-member rings by iodine anions and the quenching of electronegative carbon atoms by iodine cations, we successfully synthesize β-functionalized vinylphosphine oxides by the P-addition of QPrS intermediates generated in situ. Multiple β-iodo-substituted vinylphosphine oxides can be obtained with exceptional regio- and stereo-selectivity by reacting secondary phosphine oxides with unactivated alkynes. In addition, a variety of β-functionalized vinylphosphine oxides converted from C-I bonds, especially the rapid construction of benzo[b]phospholes oxides, demonstrates the significance of this strategy.

Effective In Situ Alkoxide Trapping by TMSX in the Presence of TPP Catalyst in Glycidol Acetal Rearrangements

This study demonstrates a nucleophile-catalyzed, trimethylsilyl halide-promoted rearrangement reaction of glycidol acetals to form halogenated cyclic acetals. The acetal group has been activated selectively in the presence of trimethylsilyl cation, which is used as in situ-generated alkoxide trapping reagent. Nucleophilic chloride and bromide ions participate in addition reactions with epoxides predominantly via SN1-type epoxide opening, while non-nucleophilic iodide and triflate ions induce a positive charge at the epoxide carbon. A systematic investigation of acetal-initiated polyene cyclization of epoxy polyenes has been conducted using bicyclic epoxonium ions as transient intermediates. Unfavorable orbital orientation and other stereoelectronic factors hinder the much-anticipated polyene cyclizations. The potential of this method has been showcased through its application in the total synthesis of parvistone A, a chlorinated styryllactone.

The Development of a Sulfamate-Tethered Aza-Michael Cyclization Allows for the Preparation of (-)-Negamycin tert-Butyl Ester

We present the first examples of intramolecular aza-Michael cyclizations of sulfamates and sulfamides onto pendant α,β-unsaturated esters, thioesters, amides, and nitriles. Stirring the substrate with catalytic quantities of the appropriate base delivers the product in good yield and excellent diastereoselectivity. The reactions are operationally simple, can be performed open to air, and are tolerant of a variety of important functional groups. We highlight the utility of this technology by using it in the preparation of a (-)-negamycin derivative.

Fun With Unusual Functional Groups: Sulfamates, Phosphoramidates, and Di-tert-butyl Silanols

Compared to ubiquitous functional groups such as alcohols, carboxylic acids, amines, and amides, which serve as central "actors" in most organic reactions, sulfamates, phosphoramidates, and di-tert-butyl silanols have historically been viewed as "extras". Largely considered functional group curiosities rather than launch-points of vital reactivity, the chemistry of these moieties is under-developed. Our research program has uncovered new facets of reactivity of each of these functional groups, and we are optimistic that the chemistry of these fascinating molecules can be developed into truly general transformations, useful for chemists across multiple disciplines. In the ensuing sections, I will describe our efforts to develop new reactions with these "unusual" functional groups, namely sulfamates, phosphoramidates, and di-tert-butyl silanols.

Ring Opening of Aziridines by Pendant Sulfamates Allows for Regioselective and Stereospecific Preparation of Vicinal Diamines

The ring opening of aziridines by pendant sulfamates is a viable strategy for the rapid preparation of vicinal diamines. Our reaction is compatible with both disubstituted cis- and trans-aziridines; unsubstituted, N-alkyl, and N-aryl sulfamates engage effectively. In all cases examined, the cyclization reaction is perfectly regioselective and stereospecific. Once activated, the product oxathiazinane heterocycles can be ring opened with a diverse range of nucleophiles.