Intramolecular hetero Diels–Alder reactions of vinyl allenes and aldehydes☆

Allenes in Diels–Alder Cycloadditions

“…Thus, reaction of 45 with 46 yields predominantly endo -adduct 48 (through preferred TS 47 ) over exo -adduct 49 , 33 and reaction of 50 (R = H or Ph) with 46 gives 51 for similar reasons. 13 The preference for endo -mode cycloadditions has been ascribed to stabilizing secondary orbital interactions (SOIs) in the transition state. 34…”

Intramolecular Hetero-Diels-Alder Reaction of Vinylallenes and Imines: Synthesis of 9-Methyl-1,2,3,4,5,6,7,8-octahydroacridine

“…The intramolecular Diels-Alder reaction is generally more favorable than the intermolecular process, mainly due to entropic reasons, 4 and although only a few examples of intramolecular Diels-Alder reaction of dienes with a carbonyl group as dienophile have been reported, 5 we decided to test the vinylallene moiety in this reaction with aldehydes as heterodienophiles. The required compounds containing the semicyclic vinylallene and the aldehyde linked by a chain of two or three carbon atoms were prepared, and it was found that the reaction took place yielding only one isomer (trans) in each case 6 due to the restrictions imposed by the length of the tether and the rigidity of the allene 7 (Equation 2). The compounds with the shorter chains were more reactive, as expected, 7 and in fact some of the reactions were spontaneous at room temperature (R = alkyl, n = 1, Equation 2).…”

Silver-Catalyzed 1,3-Acyloxy Migration/Diels–Alder Reaction of 1,9-Dien-4-yne Esters to Partially Hydrogenated Isoquinolines

“…This might be achieved by employing a silver­(I) complex instead of a gold­(I) salt as the catalyst by exploiting the significantly lower propensity of the second-row element to coordinate to the π- bonds of alkenes, alkynes, and allenes. − In doing so, we discovered the substrate to follow a reactivity pathway that was initially triggered by an 1,3-acyloxy migration to give the corresponding allenic ester. Subsequent Diels–Alder reaction of the allene motif with the allyl amine group was then found to afford the partially hydrogenated isoquinoline product. ,, Herein, we disclose the details of this rearrangement chemistry that offers a facile and chemoselective synthetic route to a new member of the partially hydrogenated N -heterocyclic family in good to excellent yields under mild conditions. Included in this are two examples containing an architecturally challenging sp 3 quaternary carbon center at one of the bridgehead positions of the bicyclic adduct as well as the gram-scale synthesis of one analogue.…”