Data on rearrangements of monoterpenoids with the Data on rearrangements of monoterpenoids with the bicyclo[4.1.0]heptane skeleton occurring by ionic, radical and bicyclo[4.1.0]heptane skeleton occurring by ionic, radical and concerted mechanisms are generalised and analysed. The biblio-concerted mechanisms are generalised and analysed. The bibliography includes 135 references graphy includes 135 references. .
Greater than 900 named fragrances are currently produced worldwide, either through synthetic pathways or by isolation from natural essential oils. The demand for synthetic fragrances in perfumery, cosmetics, and food flavors exceeds by 5-6 times the use of natural products.Herein we present results from a study of transformations of 7-methyl-2H-benzo[b][1,5]dioxepin-3(4H)-one (calone). Calone (1) or watermelon ketone was isolated from watermelon rind and is a valuable fragrance for preparing fresh, marine, and ozone aromas. Up to 25% of the worldwide assortment of modern perfumery contains calone. Calone, being an important indicator of marine aroma, contains in its molecule a constrained reaction center, the carbonyl. Performing reactions at this group enables the two methylenes immediately adjacent to the O atoms and the aromatic ring to be preserved. This is a potential feature of the marine aroma [1].Reaction of 1 with malonic acid dinitrile and cyanoacetic acid ethyl ester in the presence of piperidine and acetic acid formed the condensation products 2-(7-methyl-2H-benzo[b][1,5]dioxepin-3(4H)-ylidene)malononitrile (2) and ethyl-2-cyano-2-(7-methyl-2H-benzo[b][1,5]dioxepin-3(4H)-ylidene)acetates 3a and 3b. Malononitrile 2 with a symmetric substituent is the only reaction product whereas addition of ethyl cyanoacetate forms the cis-(3a) and trans-isomers (3b) in a 1:2 ratio. This was confirmed by PMR spectroscopy.
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