Intra- and intermolecular hetero-Diels-Alder reactions. 45. Simple and induced diastereoselectivity in intramolecular hetero-Diels-Alder reactions of 1-oxa-1,3-butadienes. Experimental data and calculations
摘要:
The simple and induced diastereoselectivity of the intramolecular hetero-Diels-Alder reaction of the alkylidene 1,3-dicarbonyl compounds 7a-e, obtained in situ by Knoevenagel condensation of the aldehydes 5a-e and dimethylbarbituric acid 6, was investigated experimentally and theoretically. In all examples the selectivity is very high; thus the domino reaction of 5a and 6 gives nearly exclusively the trans-fused tricyclic dihydropyran 8 (trans/cis = 98.8:1.2). In the similar reactions of the chiral aldehydes 5b-e and 6 the trans-cycloadducts 28, 33, 36, and 41 are the main products out of four possible diastereomers. The induced diastereoselectivity for the reaction of 5b and 5e with 6 is >99:1 and for the reaction of 5e and Sd-with 6, 95.2:3.6 and 94.1:4.7, respectively. Semiempirical AM1 calculations have been used to locate the transition structures of the intramolecular hetero-Diels-Alder reaction of 7a. The results were employed to create new parameters for the MM2-type force-field to determine the transition structures of 7b-e. The obtained data were compared with the experimental results of the cycloadditions and showed an excellent agreement.
在艾伦·弗朗西斯·托马斯(Alan Francis Thomas)首次发现五十年之后,我们描述了一种多用途,无金属且无压力的多米诺-克莱森-科普重排方法,它使用易于获得的α,β-不饱和醛5或其缩醛5'和烯丙基醇6进行重排。通过这种转换,可以方便地访问大量的辐射柑橘和花香的玫瑰味气味剂。气味新颖花香红润和柑橘醇的型材13,14,和16进行了研究。化合物14ba具有花香,玫瑰色,天竺葵般的特征,并具有独特的性能和扩散性。复合16ba具有清晰的主要柑橘香气特征,具有干净的绿色葡萄柚/大黄成分。两种香精最近已成功引入Rosyfolia ™(14ba)和Pomelol ™(16ba)香水中。