Studies On [3+3] Cyclization Of α,β-unsaturated Carbonyl Compounds

The aldehydes and ketones in basic medium give an enolate anion which acts as a nucleophilic reagent. In addition, they react with nucleophiles that are related to deficient carbon. It is therefore not surprising that in a basic medium, an aldehyde or ketone having at least one hydrogen atom in α-position reacts on itself in the absence of any other reagent. The enolate formed from a first molecule is added to the carbonyl group of another molecule. In a broader sense the carbonyl compounds for example esters, amides, carboxylates condense with aldehydes or ketones to giveβ-hydroxy-carbonyl compounds which in turn eliminate a water molecule to form α,β-unsaturated carbonyl compounds. These have been used as efficient methods in [3+3] cycloadditions. Such reactions have been widely used both in the synthesis of natural products and the synthesis of six-membered cyclic compounds. However, majority of the synthetic applications of of α,β?-unsaturated carbonyl compounds were focused on the synthesis of heterocycles like pyrroles, indoles, furans, pyrans, piperidine, pyridine, benzofurans, thiophenes and benzothiophenes.The formation of multisubstituted benzene compounds via [3+3] or [3+2+1] cycloaddition based on α,β-unsaturated carbonyls has been reported rarely. Although these approaches have contributed to the development of the synthetic pathway for the synthesis of various substituted benzenes, to our knowledge, there has been no report on the synthesis of polysubstituted benzenes from commercially available starting materials in a single step under mild conditions with the advantage of environmentally benign, atom and energy-efficient processes that do not rely on toxic/precious metals.Thus, during our research we have developed the Synthesis of polysubstituted benzene derivatives from a-oxo-ketene dithioacetals with ethyl4-(S,S-dimethylbromothio)crotonate via [3+3] cycloaddition approach under mild conditions. Although, a few synthetic approaches for the construction of this kind of cycloaddition have been reported but most of them many suffer from long sequences of reactions in several stages with lowest yields.We developed a new efficient way for the synthesis of polysubstituted benzene compounds in high yields from the sequential addition reaction of Michael, nucleophilic cyclization, condensation and oxidation followed by aromatization of α,β-unsaturated carbonyl compounds, a readily available raw material with dimethyl glutaconate, commercially available, in the presence of sodium hydroxide as catalyst under mild conditions. These benzene compounds were characterized by all spectral analysis whose data were recorded in this present work.