[4 + 2]‐Cycloadditionen mit 5‐Ethenyl‐3,4‐dihydro‐2H‐pyran und 5‐Ethenyl‐2,3‐dihydro‐1,4‐dioxin

Abstract

4 + 2]-Cycloadditions with 5-Ethenyl-3,4dihydro-2H-pyran and 5Ethenyl-2,3-dihydro-l,4dioxine S-Ethenyl-3,4-dihydro-2H-pyran (2a) and 5-ethenyl-2,3-dihydro-l,4dioxine (2 b) as heterocyclic donor-activated 1,3-dienes are prepared by Wittig alkenylation of the aldehydes l a and 1 b. [4 + 21-Cycloadditions with dienophiles such as tetracyanoethene, p-nitrostyrene, diethyl azodicarboxylate, phenyltriazolinedione, and diethyl mesoxalate yield the new heterobi-and -tricycles 3-7. a: X = CH2 b : X = O l a , b 40 A0A 0 20, b 7 6 a , b N II N C02C2H5 5 a , b 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1986

Copper‐Catalyzed Alkenylation and Alkenyloxylation with‐Alkenyl(phenyl)iodonium Salts

“…To showcase its synthetic utility, we successfully obtained 3 a and 6 a in a gram‐scale synthesis (Scheme 6a). Furthermore, 3 m underwent [4+2] Diels‐Alder reaction with dienophiles to construct heteroatom‐containing cyclic compounds 8, yielding an impressive 82% yield [21] . Considering the Diels‐Alder reaction mechanism, the primary diastereomer of 8 is cis.…”

“…Furthermore, 3 m underwent [4 + 2] Diels-Alder reaction with dienophiles to construct heteroatom-containing cyclic compounds 8, yielding an impressive 82% yield. [21] Considering the Diels- [a] Reaction conditions: 1 a (0.3 mmol, 1.5 equiv. ), 5 a (0.2 mmol, 1.0 equiv.…”

Selective Hydrodeoxygenation of Cyclic Vicinal Diols to Cyclic Alcohols over Tungsten Oxide–Palladium Catalysts

“…The additional advantage of using unactivated olefins is that various synthetically useful transformations like carbonyl insertions are also feasible, which enhances the scope and utility of the methodology. The resulting electron‐rich dienes are potential partners in Diels–Alder cycloadditions,15 which can give rise to interesting molecular frameworks and thereby are proposed as potential building blocks in many polyether‐type natural products containing the pyran skeleton.…”

The Enantiomeric Scaffold Approach to Highly Functionalized 1-Oxadecalines: Enantio- and Regiocontrolled [4 + 2] Cycloadditions of 5-Alkenyl-η3-Pyranylmolybdenum Complexes

“…For example, cycloadditions of 5-vinyl-2,3-dihydro-4H-pyran have been described only with highly electrophilic dienophiles such as tetracyanoethylene, N-phenyltriazolinedione or diethyl azodicarboxylate. 12 Despite low reactivity, high diastereoselectivity was observed in the intermolecular DielsAlder reaction of enantiomerically pure dienes such as those depicted in Figure 2 ,13-16 and other related 1-oxapyranyl dienes. [17][18][19][20] The use of Lewis acid promoters to enhance the reactivity of dienophiles with these pyranyl dienes remains largely unexplored, most likely due to the low reactivity of the dienes and their high propensity to decompose in the presence of Lewis acids.…”

“…Moreover, the corresponding Diels−Alder reaction of pyranyl-based dienes with electron-deficient alkenes is limited to highly electrophilic dienophiles, such as maleimides or maleic anhydride, most likely due to the poor reactivity associated with these types of dienes under thermal conditions. For example, cycloadditions of 5-vinyl-2,3-dihydro-4 H -pyran have been described only with highly electrophilic dienophiles such as tetracyanoethylene, N -phenyltriazolinedione, or diethyl azodicarboxylate . Despite low reactivity, high diastereoselectivity was observed in the intermolecular Diels−Alder reaction of enantiomerically pure dienes, such as those depicted in Figure , − and other related 1-oxapyranyl dienes. − The use of Lewis acid promoters to enhance the reactivity of dienophiles with these pyranyl dienes remains largely unexplored, most likely due to the low reactivity of the dienes and their high propensity to decompose in the presence of Lewis acids.…”