Synthesis of functionalized hexahydro-, octahydro-, and decahydro-1H-phenalenes via Diels–Alder reactions of 1-methylene-4a-methoxycarbonyl-1,2,3,4,4a,5,6,7-octahydronaphthalene and related dienes

Abstract

The results of a study of Diels–Alder reactions of the bicyclic dienes 6–8 with a variety of dienophiles are reported. Although 6 and 7 undergo cycloaddition reactions smoothly and efficiently, thermal Diels–Alder reactions of 8 are generally sluggish or, under the conditions investigated, do not proceed at all. Additions of tetracyanoethylene (TCNE) to 6–8 are highly face-selective, with preferential attack of the dienophile on the side of the dienes opposite to the angular methoxycarbonyl group. Reaction of 7 with maleic anhydride (MAN) is completely face-selective and proceeds preferentially via an endo transition state. Diels–Alder reactions of 6 and 7 with methyl acrylate (MAC) and nitroethylene (NE) are entirely regioselective, but the face-selectivities, which vary from ~2:1 to ~3:1, are rather low. The use of this chemistry as a method for the synthesis of functionalized, stereochemically defined, perhydro-1H-phenalenes is demonstrated.

Preparation of phenalenes and hydronaphthacenes through tandem alkyne Fischer–carbene complex coupling and inter- or intra-molecular Diels–Alder reactions

“…6 The phenalene ring system is most commonly accessed through intramolecular electrophilic aromatic substitution reactions 7 and occasionally through Diels-Alder processes. 8 The phenalene ring system is potentially accessible in a single reaction event through a recently-discovered sequence involving tandem carbene complex alkyne coupling 9 / isobenzofuran formation 10 / and Diels-Alder reaction (Scheme 1). 11 Operationally this is a very simple process involving only thermolysis and avoids a multi-step series of reactions required to perform similar transformations without chromium.…”