We describe the first efficient oxidation of homoallylic and homopropargylic alcohols to the corresponding very sensitive and unstable b,g-unsaturated aldehydes by using the Dess-Martin periodinane with a new neutral and anhydrous extraction protocol.Homoallylic and homopropargylic aldehydes are very interesting key intermediates in total synthesis. Especially (Z)-b,g-ethylenic aldehydes are used intensively to produce, via cis Wittig olefination, characteristic the (Z,Z)-1,4-dienic moiety of the polyunsaturated fatty acids (PUFAs), analogs or metabolites. 1 On the other hand, the corresponding b,g-acetylenic aldehydes which are very unstable due to the acidity of the propargylic hydrogens, exhibit a high potential in synthesis but are described in only few papers in the literature. 2,3 We have previously prepared these aldehydes using either mild hydrolysis of b,g-ethylenic 4 or b,g-acetylenic acetals; 3 other groups have proposed the oxidative cleavage of homoallylic 5 or homopropargylic diols 2 and the direct oxidation of the corresponding alcohols 6 (Scheme 1). The first two furnish a clean b,g-unsaturated aldehyde under the appropriate mild conditions without isomerization or migration of the unsaturated bond.Although the direct oxidation of b,g-unsaturated alcohols looks to be the approach of choice, to our knowledge, the method has never been described for homopropargylic alcohols. This process has been sometimes applied successfully for the preparation of various b,g-ethylenic aldehydes. 7,8 However, the main drawback is the partial or total migration of the double bond to form the corresponding more stable a,b-unsaturated aldehydes. 5d,6a,9 Scheme 1Our interest in b,g-unsaturated aldehyde precursors of the n-3 and n-6 series of PUFA's and their derivatives 4 led us to study the oxidation of (Z)-hex-3-enol, (Z)-non-3-enol and the corresponding acetylenic alcohols. Herein, we describe our results using the Dess-Martin periodinane (DMP). 10 Among the numerous useful oxidation methods described in the literature for many years, 11 Dess and Martin proposed one of the mildest and selective one for primary and secondary alcohols. 12 From these first papers, the DMP received a wide attention for the oxidation of various sensitive substrates to prepare epimerizable aldehydes, 13 allylic aldehydes, 5e,14 some homoallylic aldehydes, 7 perfluoroalkyl aldehydes 15 from alcohols, carbonyl compounds from oximes, 16 cyclic enecarbamates from w-hydroxycarbamates, 17 and acylnitroso compounds from nacylhydroxylamines. 18 New reactions have also been discovered with various a,w-diols, 19 unsaturated glycols, 20 arylamines 21 or anilides. 22The DMP may be either purchased or prepared according to known procedures 23 that are slight modifications of those proposed by Dess and Martin. 12 The preparation of the DMP from cheap starting materials makes this reagent very interesting and challenging. The main features of the DMP oxidation are the neutral conditions used for the reaction and the work up.Our first goal was the prep...

The transformation of easily accessible 2‐vinylidenehydrofurans into stable 1,3‐dienes has been achieved by using catalytic amounts of palladium(0). These valuable compounds were then engaged in subsequent Diels–Alder reactions giving access to complex heterocyclic cores found in numerous natural products. A rationale for the regioselectivity of the Diels–Alder reactions with vinylfurans has been provided by DFT calculations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

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P a l l a d i u m ( 0 ) -C a t a l y z e d I s o m e r i z a t i o n o f 2 -V i n y l i d e n e h y d r o f u r a n s Abstract: Highly sensitive functionalized 2-vinylidene-hydrofurans undergo a facile, clean and chemoselective Pd(0)-catalyzed isomerization leading to stable and valuable 3-oxa-1,3-dienes precursor of polycyclic systems found in bioactive natural products through Diels-Alder reaction.

2005 Furan derivatives R 0060Facile, Efficient and Chemoselective Palladium(0)-Catalyzed Isomerization of 2-Vinylidenehydrofurans into Valuable Functionalized 1,3-Dienes. -In the presence of Pd(O-Ac)2/dppp, the title compounds undergo facile, clean, and chemoselective isomerization to synthetically important 3-oxa-1,3-dienes. The benzofuran skeletons (X) and (XII) are found in various bioactive compounds or natural products. -(WAVRIN, L.; NICOLAS, C.; VIALA*, J.; RODRIGUEZ*, J.; Synlett 2004, 10, 1820-1822; Lab. SymBio, Cent. St. Jerome, Univ. Paul Cezanne, F-13397 Marseille, Fr.; Eng.) -Jannicke 01-094