Facile synthesis of 4,5,6a,7-tetrahydrodibenzo[de,g]chromene heterocycles and their transformation to phenanthrene alkaloids

Synthesis of functionalised isochromans: epoxides as aldehyde surrogates in hexafluoroisopropanol

The oxa-Pictet-Spengler reaction is arguably the most straightforward and modular way to construct the privileged isochroman motif, but its scope is largely limited to benzaldehyde derivatives and to electron-rich β-phenylethanols that lack substitution along the aliphatic chain. Here we describe a variant of this reaction starting from an epoxide, rather than an aldehyde, that greatly expands the scope and rate of the reaction (<1 h, 20 °C). Besides facilitating the initial Meinwald rearrangement, the use of hexafluoroisopropanol (HFIP) as a solvent expands the electrophile scope to include partners equivalent to ketones, aliphatic aldehydes, and phenylacetyl aldehydes, and the nucleophile scope to include modestly electronically deactivated and highly substituted β-phenylethanols. The products could be easily further derivatised in the same pot by subsequent ring-opening, reductions, and intra- and intermolecular Friedel-Crafts reactions, also in HFIP. Finally, owing to the high pharmacological relevance of the isochroman motif, the synthesis of drug analogues was demonstrated.

Synthesis of di-, tri- and tetracyclopropylhydrazines

Previously unknown 1,1-dicyclopropylhydrazine was obtained in two steps starting from dicyclopropylamine. It serves as a convenient starting material to tri- and tetracyclopropylhydrazines, which have not been described in the literature either. Tricyclopropylhydrazine was prepared in an overall four-step sequence featuring the de Meijere-Chaplinski modification of the Kulinkovich reaction as a key step. Tetracyclopropylhydrazine was obtained by the reductive amination of the cyclopropanone ethyl trimethylsilyl acetal with 1,1-dicyclopropylhydrazine or with the parent hydrazine. Synthetic utility of these cyclopropylhydrazine building blocks is presented as well.

Evaluation of structural effects on 5-HT(2A) receptor antagonism by aporphines: identification of a new aporphine with 5-HT(2A) antagonist activity

A set of aporphine analogs related to nantenine was evaluated for antagonist activity at 5-HT2A and α1A adrenergic receptors. With regards to 5-HT2A receptor antagonism, a C2 allyl group is detrimental to activity. The chiral center of nantenine is not important for 5-HT2A antagonist activity, however the N6 nitrogen atom is a critical feature for 5-HT2A antagonism. Compound 12b was the most potent 5-HT2A aporphine antagonist identified in this study and has similar potency to previously identified aporphine antagonists 2 and 3. The ring A and N6 modifications examined were detrimental to α1A antagonism. A slight eutomeric preference for the R enantiomer of nantenine was observed in relation to α1A antagonism.