Recent investigations have shown the particular utility presented by certain organo-selenenyl derivatives as selected intermediates in various syntheses. More precisely, it could be established that certain .beta.-hydroxy-selenenyl compounds of formula ##STR1## wherein R' defines a lower alkyl radical or an aryl group and R.sup.1, R.sup.2 and R.sup.3 each represents an alkyl radical or a hydrogen atom, constitute very useful starting materials for the preparation of allyl alcohols, epoxydes or olefines [see e.g.: J. Amer. Chem. Soc., 95, 2697 (1973); Angew. Chem. Int. Ed. 13, 804 (1974); idem 13, 805 (1974); Tetrahedron Letters, 1385 and 3743 (1976); J. Chem. Soc. Chem. Comm. 790 (1975); Angew. Chem. Int. Ed. 14, 700 (1975)].
Said .beta.-hydroxy compounds could be synthesized by a regiospecific and stereoselective synthesis starting from an .alpha.-seleno-aldehyde or -ketone by reduction with lithium aluminiumhydride or by means of a Grignard type reagent [see: Tetrahedron Letters, 3227 (1976)].
.alpha.-Seleno-aldehydes and .alpha.-seleno-ketones have been prepared in the past via the process described by K. B. Sharpless et al., namely as described in J. Amer. Chem. Soc., 95, 6137 (1973). According to these authors, .alpha.-phenyl-seleno-carbonyl derivatives of formula ##STR2## wherein symbol R represents an alkyl or an aryl radical and X defines a hydrogen atom or an alkyl group, can be obtained by treating a ketone or an aldehyde with the reagents such as phenyl-selenenyl chloride or bromide.
By applying this process to the synthesis of the desired selenenyl derivative of acetaldehyde, one is faced with major difficulties. The reaction in fact ought to be carried out in a strongly acidic medium and it is known that under these reaction conditions, acetaldehyde undergoes aldolisation, hence a marked reduction in the yield of the end products.