Synthesis of (tetrahydrofuran-2-yl)acetates based on a ‘cyclization/hydrogenation/enzymatic kinetic resolution’ strategy

Small and Smart: Adventures in Epihalohydrin Chemistry

The present personalized account aims to highlight reactions of epichlorohydrin and epibromohydrin with free and masked dianions. These reactions permit convenient syntheses of a variety of products, such as 2-(alkylidene)tetrahydrofurans (which can be further functionalized by hydrogenation or ring-transformation reactions), cyclopropanes, γ-butyrolactams, oxazines, oxazolo[3,4-b]pyridazin-7-ones, or 2-(alkylidene)thiazolidines. In general, the reactions proceed with very good regioselectivity.

1 Introduction

2 Reactions of Masked Dianions

2.1 Synthesis of 2-(Alkylidene)tetrahydrofurans

2.2 Functionalization of 2-(Alkylidene)tetrahydrofurans

3 Reactions of Free Dianions

3.1 Synthesis of 2-(Alkylidene)tetrahydrofurans

3.2 Functionalization of 2-(Alkylidene)tetrahydrofurans

3.3 Synthesis of γ-Butyrolactams

3.4 Synthesis of 5,6-Dihydro-4H-1,2-oxazines

3.5 Synthesis of Oxazolo[3,4-b]pyridazin-7-ones

3.6 Synthesis of Cyclopropanes

3.7 Synthesis of 2-(Alkylidene)thiazolidines

4 Conclusions

2-(Tetrahydrofuran-2-yl)acetic Acid and Ester Derivatives as Long-Range Pollinator Attractants in the Sexually Deceptive Orchid Cryptostylis ovata

Sexually deceptive orchids achieve pollination by luring male insects to flowers through chemical and sometimes visual mimicry of females. An extreme example of this deception occurs in Cryptostylis, one of only two genera where sexual deception is known to induce pollinator ejaculation. In the present study, bioassay-guided fractionations of Cryptostylis solvent extracts in combination with field bioassays were implemented to isolate and identify floral volatiles attractive to the pollinator Lissopimpla excelsa. ( S)-2-(Tetrahydrofuran-2-yl)acetic acid [( S)-1] and the ester derivatives methyl ( S)-2-(tetrahydrofuran-2-yl)acetate [( S)-2] and ethyl ( S)-2-(tetrahydrofuran-2-yl)acetate [( S)-3], all previously unknown semiochemicals, were confirmed to attract L. excelsa males in field bioassays. Chiral-phase GC and HPLC showed that the natural product 1 comprised a single enantiomer, its S-configuration being confirmed by synthesis of the two enantiomers from known enantiomers of tetrahydrofuran-2-carboxylic acid.

Effective Synthesis of a Novel Tetrahydrofuran Containing Triterpenoid: 5′(Z)-Benzylidene-tetrahydrofurano[3,2-b]lup-20(29)-en-28-oate

The title compound 5′(Z)-benzylidene-tetrahydrofurano[3,2-b]lup-20(29)-en-28-oate was synthesized with high chemo-, regio-, and stereoselectivity by 5-exo-dig cycloisomerization of methyl 2α-phenylpropynyl-3-oxolup-20(29)-en-28-oate with use of KN(SiMe3)2-DME. The novel betulinic acid derivative was fully characterized by conventional analytical methods and all proton and carbon signals have been completely assigned by 2D-NMR experiments.

Asymmetric Catalysis via Cyclic, Aliphatic Oxocarbenium Ions

A direct enantioselective synthesis of substituted oxygen heterocycles from lactol acetates and enolsilanes has been realized using a highly reactive and confined imidodiphosphorimidate (IDPi) catalyst. Various chiral oxygen heterocycles, including tetrahydrofurans, tetrahydropyrans, oxepanes, chromans, and dihydrobenzofurans, were obtained in excellent enantioselectivities by reacting the corresponding lactol acetates with diverse enol silanes. Mechanistic studies suggest the reaction to proceed via a nonstabilized, aliphatic, cyclic oxocarbenium ion intermediate paired with the confined chiral counteranion.

Chemoselective intramolecular alkylation of the Blaise reaction intermediates: tandem one-pot synthesis of exo-cyclic enaminoesters and their applications toward the synthesis of N-heterocyclic compounds

The intramolecular alkylative reactivity and N/C selectivity of the various Blaise reaction intermediates, which are formed from the reaction of the Reformatsky reagents with ω-chloroalkyl nitriles, did not reach the synthetic potential as an entry to exo-cyclic enaminoesters. To circumvent this issue, various additives were investigated, among which the addition of NaHMDS dramatically enhanced the reactivity and N/C selectivity. This modification provided a highly efficient route for the synthesis of various N-fused heterocyclic compounds, as it requires only two steps from nitriles.