Two different synthetic pathways are presented that provide access to enantiopure sulfinyl hydrazones; in both addition of sulfenic acid/unsaturation represents the crucial step of the procedure. The obtained results are discussed in terms of regioselectivity in the formation of a-and/or b-sulfinyl a,b-unsaturated products when sulfenic acids are reacted with substrates showing carbonyl conjugated triple bonds, and/or their derivatives. Despite its structural limitations, (R S ,E,E)-2-[(1S)-isoborneol-10-sulfinyl]-2-butenal dimethylhydrazone (6) behaves as 1-azabuta-1,3-diene in hetero Diels-Alder reaction with N-methylmaleimide, giving a unique cycloadduct with complete endo and facial selectivities.Cyclic structures represent a relevant portion of the skeleton of several natural substances. Six-membered rings are building blocks in carbohydrates, alkaloids, terpenes, steroids, and a tremendous number of other biomolecules. Their widespread presence in nature represents the main reason for the interest generated by reactions such as the Diels-Alder (DA) cycloaddition which supplies a straightforward and stereocontrolled access to six-membered cyclic molecules.The development of an efficient and original methodology to generate a diene skeleton, bearing an enantiopure sulfinyl group, 1 directed our research towards DA reactions of such substrates with commonly used dienophiles, with the aim of testing the efficiency -as chiral auxiliary -of the sulfoxide substituent directly linked to a diene carbon, and possibly obtaining functionalized six-membered rings in enatiomerically pure form. The high degree of stereochemical control observed in the cycloadditions of diene 1 with methyl acrylate in the presence of LiClO 4 (Scheme 1) 2 prompted us to involve several different sulfinyl dienes in catalyzed and uncatalyzed homo-DA reactions. 3 We were also interested in investigating the reactivity of our sulfinyl dienes in hetero-DA (HDA) cycloadditions, which give an easy access to very useful heterocyclic molecules. Pyranoid 4 and thiopyranoid 5 derivatives 2-5 were synthesized following the approaches shown in Scheme 1. The most common heterodienophiles such as glyoxylates for pyranoid and thioketones for thiopyranoid systems cycloadded to suitable sulfinyl dienes with a satisfying stereochemical control and/or easy separation of the diastereomeric cycloadducts by chromatography. On the other hand, the facile access to high yields of enantiomerically pure b-sulfinyl a,b-unsaturated carbonyl compounds suggested their use as heterodienes in inverse electron-demanding DA reactions, giving an alternative access to enantiopure pyranoid systems (see, for instance, the synthesis of 3 in Scheme 1). 6 Scheme 1In this paper we discuss the effectiveness of the synthetic pathways a and b (Scheme 2) towards enantiopure sulfinyl a,b-unsaturated dimethylhydrazones, obtained by addition of suitable sulfenic acids to alkynyl hydrazones (pathway a) or alternatively by addition of sulfenic acids to alkynyl carbonyl compounds and subseque...