Synthesis, characterization, and DFT studies of novel spiroacenaphthylene-1,3-oxazines

The novel spirocyclic 1,3-oxazino and 1,2'-pyrido systems were synthesized by [4 + 2] cycloaddition reaction between Huisgen 1,4-dipoles (isoquinoline-acetylenic esters and quinoline-acetylenic esters) with the C=O and C=C (CN)(2) double bonds of acenaphthoquinone-malononitrile adduct. The major product was the 1,3-oxazino derivative. The structure of a typical product was confirmed by X-ray crystallography. The B3LYP/6-31G(d) density functional theory calculations for carbon atom charge of keto-carbonyl group and its adjacent carbon atoms show that the carbonyl group is much more electrophilic. The major and minor products possess 2 stereogenic centers; thus, 2 diastereomers are possible for each compound. The calculated energy difference between [(1R,11bS)/(1S,11bR)] and [(1R,11bR)/(1S,11bS)] diastereomers of major product is 8.8 kcal/mol, while the more stable diastereomer of minor product [(1S,11bS)/(1R,11bR)] is calculated to have 9.9 kcal/mol lower energy than [(1S,11bR)/(1R,11bS)] isomer. The diastereoselectivity, good yields, and lack of activator or metal promoters are the main advantages of this approach.