Useful base promoted elaborations of oxiranyl ethers

doi:10.1016/S0040-4020(01)00790-6

Tetrahedron

Volume 57, Issue 38, 17 September 2001, Pages 8173-8180

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Abstract

Functionalized oxiranyl ethers can be regio- and stereoselectively converted into hydroxy oxetanes or cis-diols by treatment with organometallic bases. These two rearrangements can be conveniently carried out either using different reaction conditions starting from the oxirane or in two consecutive steps from the oxirane via the oxetane.

Graphic

Introduction

We have shown in the last few years that oxiranyl ethers 1 can be conveniently elaborated in a number of ways, to afford useful building blocks such as hydroxyvinyl ethers 2,1., 2., 3., 4. hydroxyoxetanes 3,5., 6., 7. diols 4,⁸ allylic alcohols 5⁹ and hydroxytetrahydrooxepines 6¹⁰ (Scheme 1, routes a–f, respectively).

All these transformations have been carried out making use of superbases11., 12. and in particular an equimolar mixture of butyllithium, diisopropylamine and potassium tert-butoxide (LIDAKOR)¹³ except for the preparation of allylic alcohols which occurs by reductive lithiation¹⁴ of the thiophenyl substituted epoxy ether with the radical anion LDBB¹⁵ via Grob-type fragmentation.16., 17.

Section snippets

Results and discussion

Due to the synthetic utility of oxetanes,18., 19. their preparation is still of interest. Furthermore, the recently reported novel stereoselective rearrangement of oxiranes (1) or oxetanes (3) into Z-2-alkene-1,4-diols (4) worked only in those cases when R and Y were alkyl and phenyl groups, respectively.⁸ The phenyl group is a requisite of the rearrangement process. However, this new reaction would be a convenient route to practically useful building blocks (type 4) of biologically active

General

Air and moisture sensitive compounds were stored in Schlenk tubes or in Schlenk burettes. They were protected by and handled under an atmosphere of 99.99% pure nitrogen. Ethereal extracts were dried with sodium sulfate. The temperature of dry ice–ethanol baths is consistently indicated as −78°C, that of ice bath as 0°C and ‘room temperature’ as 25°C. If no reduced pressure is specified, boiling ranges were determined under ordinary atmospheric conditions (720±35 mmHg). Purifications by flash

Acknowledgements

The authors are indebted to the CNR (Italy) and the Hungarian Academy of Sciences for promotion of the scientific cooperation in the framework of the bilateral cooperation agreement between the two institutions. This research work was supported by the National Research Foundation of Hungary (OTKA Grant No. T-030803).

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The present study reports regio- and highly diastereoselective preparative methods for the synthesis of versatile alkaloid-type compounds from oxiranylmethyl tetrahydroisoquinolines. 2,5-Methanobenzo[c]azepines or azetidine-fused heterocycles were synthesized in tandem reactions depending on the absence or presence of a BF₃ co-reagent. A high functional group tolerance has also been demonstrated. DFT calculations with an explicit solvent model confirmed the proposed reaction mechanisms and the role of kinetic controls on the stereochemical outcome of the reported new methods.
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Next, an intramolecular nucleophilic reaction occurs between the alkalibenzyl moiety and the electrophilic C2 carbon atom of the oxirane ring resulting in simultaneous ring opening of the three membered heterocycle and the formation of the azetidine ring (4-exo ring closure, Scheme 5). The proposed reaction mechanism is analogous with the transformations of the benzyloxymethyl group containing oxiranes into oxetanes21,22 and provides such azetidines in which the C2 and C3 substituents are positioned (Scheme 7) on the opposite side of the ring (in a trans-position to each other). Spectroscopic investigations of products 10–13 confirmed that the C2 and C3 substituents were always situated in a trans-position around the azetidine ring, that is, the new azetidine forming reaction is stereoselective.
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There are several protein kinase C enzyme inhibitors among the optically active, 3,4-disubstituted pyrrolidines used in the treatment of certain cancer diseases [2]. Previously we reported a method, in which aminooxetanes could stereoselectively be obtained from chiral disubstituted oxiranes in the presence of potassium tert-butoxide activated lithium diisopropylamide (LiDA–KOR) [3]. Furthermore, pure enantiomers of 3-[1′-hydroxy-2′-(dibenzylamino)ethyl]-2-phenyloxetane were synthesized from cis-4-benzyloxy-2,3-epoxybutanol using enzymatic kinetic resolution followed by consecutive tosylation, dibenzylamination and organometallic base promoted enantioselective rearrangement reactions [4].
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Useful base promoted elaborations of oxiranyl ethers

Abstract

Introduction

Section snippets

Results and discussion

General

Acknowledgements

Tetrahedron Lett.

Tetrahedron: Asymmetry

Tetrahedron

J. Organomet. Chem.

Tetrahedron Lett.

Tetrahedron. Lett.

Tetrahedron

Tetrahedron

J. Org. Chem.

Synlett

J. Org. Chem.

J. Org. Chem.