A convenient procedure for the synthesis of highly enantioenriched allenylsilanes by Johnson orthoester Claisen rearrangement of 1-silyl propargylic alcohols is described. Allenylsilanes are then used as carbon nucleophiles in three-component, Lewis acid mediated additions to in situ generated oxonium ions, resulting in enantioenriched homopropargylic ethers.

Allenylsilanes are used as carbon nucleophiles in highly stereoselective Lewis acid-promoted C-glycosidations, resulting in the introduction of an internal alkyne with an adjacent stereocenter. Both achiral and chiral allenylsilanes form the desired products with high diastereoselectivity, where the nucleophile adds exclusively to the α-face of the intermediate oxonium ion. Reactions with glucal and galactal afford dihydropyran products, while reactions with a ribose derivative yield dihydrofuran products.

Enantioenriched allenylsilanes are used as carbon nucleophiles in three component reactions with in situ generated N-sulfonylimines to selectively form syn-homopropargylic sulfonamides. The reactions proceed with a variety of aldehyde and sulfonamide reaction partners. These novel reaction products are obtained with useful levels of diastereoselectivity, and the axial chirality of the allenylsilane is fully transferred to point chirality, forming products with >97% ee.Recent developments in the synthesis and use of allenylmetal reagents have allowed their reemergence as an important class of reagents for a variety of organic transformations, capable of producing highly functionalized alkynes and heterocycles. 1 In particular, allenylsilanes have been used as carbon nucleophiles in additions to a variety of oxonium ions, producing homopropargylic alcohols, 2 homopropargylic ethers, 3 furans, 4 and dihydrofurans. 5 In cases where enantioenriched allenylsilane reagents were used, the axial chirality of the allene was typically fully transferred into point chirality in the products, leading to a variety of highly enantioenriched building blocks for organic synthesis.The reaction of allenylmetal reagents with iminium ions has been underdeveloped. The addition of allenylsilanes to N-acyl iminium ions has been shown to favor either a [3 + 2] annulation pathway, providing dihydropyrroles, or a [3 + 3] pathway to provide dihydrooxazines.5 , 6 Achiral allenylsilanes and stannanes have also been used in a [3 + 2] annulation with a N-sulfonylimines, 7 and in the case of the stannane 7a the formation of the acyclic propargylation product was favored under certain reaction conditions. In these reported cases, a single imine reaction partner was used. Experiments with allenylboranes have been shown to specifically form homopropargylic amines, 8 and in one case where enantioenriched allenylboranes were used, highly enantioenriched products were obtained. 9 * panek@bu.edu . Supporting Information AvailableExperimental data and selected spectral data for all new compounds. This material is available free of charge via the internet at http://pubs.acs.org. In our continued interest in developing chiral carbon nucleophiles as reagents to enhance the field of acyclic stereocontrol, we sought to acquire a method for the synthesis of homopropargylic amines from enantioenriched allenylsilanes. We have previously reported a multigram synthesis of enantioenriched allenylsilane 1. 3 In exploring the [3 + 2] annulation of this reagent with N-acyl iminium ions we learned that the acyclic propargylation product was obtained as a byproduct under certain conditions. This led us to seek reaction conditions that would selectively lead to homopropargylic amines. Herein we report the achievement of that objective, forming the desired products in high yields with full transfer of chirality (axial to point), thereby complementing existing methods utilizing allyl and crotyl silanes that produce homoallylic amines. 10 When allenylsilane (S a...

Enantioenriched allenylsilanes are used in three component propargylation reactions with aldehydes and silyl ethers to form syn-homopropargylic ethers that contain an imbedded azide. These materials then undergo thermally induced intramolecular 1,3-dipolar cycloaddition reactions, resulting in unique fused ring systems containing 1,2,3-triazoles. The ability to modify all three components of the reaction allows for expedient access to compounds containing significant structural and stereochemical variation.

A rhodium(II) catalyzed nitrene-alkyne cycloaddition of stereochemically well-defined homopropargylic ethers is followed by arene cyclopropanation to afford unique tetracyclic norcaradiene products bearing a cyclic sulfamate. Products from the arene cyclopropanation (Buchner reaction) can be converted to fused cycloheptatrienes via a ring enlarging electrocyclization after nucleophilic ring opening of the cyclic sulfamate ester.