The past decade of organic chemistry may be charcterized as a period of violent development of new synthetic methods. This was accompained by a systematization of the analysis of synthetic problems (synthetic strategy). The planning of the synthesis of an organic target molecule is greatly facilitated by distinguishing between reagents X(C)n … with normal reactivity (acceptor properties at C1,3,5…, donor properties at X, C2,4…) and with reactivity umpolung (acceptor properties at X, C2,4…, donor properties at C1,3,5…). In this context, reactivity umpolung turned out to be useful as a heuristic principle, as a classification scheme, and as an aid for locating so-called strategic bonds (synthon, transform, and antithesis according to E. J. Corey). There are six principal methods of umpolung: 1 2n-oxidation, heteroatom exchange and modification, homologation and its reversal, the cyclopropane “trick”, use of acetylenes, and redox reactions; under certain circumstances none of these techniques is necessary in cases where direct umpolung is possible. Throughout the article, normal reactivity is indicated by green print; reactivity umpolung by red print.

Methods of Reactivity Umpolung

2. Essential Components: Earlier Developments 5449 2.1. Activated alkenes/alkynes 5450 2.1.1. Acyclic activated alkenes/ alkynes 5450 2.1.2. Cyclic activated alkenes 5451 2.2. Electrophiles 5451 2.3. Catalysts 5452 3. Essential Components: Recent Developments 5452 3.1. Activated Alkenes/Alkynes 5452 3.2. Electrophiles 5460 3.3. Catalysts 5477 4. Asymmetric Baylis-Hillman Reaction: Earlier Developments 5495

Recent contributions from the Baylis-Hillman reaction to organic chemistry.

In den letzten zehn Jahren haben sich die organisch-chemischen Synthesemethoden sturmisch entwickelt. Parallel dazu ist die Analyse synthetischer Probleme systematisiert worden (Syntheseplanung). Die Aufstellung eines Syntheseplans fur ein organisches Zielmolekul wird durch die Unterscheidung von Reagentien X(C)n … normaler Reaktivitat (Acceptoreigenschaften an C1, 3, 5 …, Donoreigenschaften an X, C2, 4…) und umgepolter Reaktivitat (Acceptoreigenschaften an X, C2, 4 …, Donoreigenschaften an C1, 3, 5 …) bedeutend erleichtert. Die Umpolung der Reaktivitat wurde als nutzliches heuristisches Prinzip, als Einteilungsschema und als Leitfaden zum Auffinden strategischer Bindungen erkannt (Synthon-, Transform- und Retrosynthesebetrachtungen nach Corey). Die Methoden der Umpolung lassen sich in sechs Gruppen einteilen: die 1, 2n-Oxidation, den Heteroatom-Austausch, die Homologisierung und ihre Umkehr, den Cyclopropan-„Trick”, die Verwendung von Acetylenen und die Redoxreaktionen; die in speziellen Fallen mogliche, direkte Umpolung kommt ohne diese Methoden aus. – In diesem Aufsatz wird die normale Reaktivitat durch grunen Druck, die umgepolte Reaktivitat durch roten Druck gekennzeichnet.

Methoden der Reaktivitätsumpolung

Radical reactions in organic synthesis

Stereocontrol in the synthesis of acyclic systems: applications to natural product synthesis

The odor principle β-damascenone and its isomer α-damascenone have been prepared by treatment of the corresponding ethyl safranates with excess allyl lithium followed by alkoxide catalyzed isomerization of the resulting products with β, γ-unsaturated ketonic side chains Addition of allyltriphenylphosphorane (preferably prepared from allyltriphenylphosphonium chloride) rather than the propenyl isomer to ethyl α-isopropylidene-acetoacetate produced ethyl α-safranate This represents a new, potentially general method for the synthesis of functionalized cyclohexadienes

Synthetic Studies on Damascenones

Ozonolysis of vinylsilanes

Conversion of allylic alcohols to homologous amides by N,N-dimethylformamide acetals

β-Sinensal, a flavor constituent of the Chinese orange, has been synthesized from myrcene by a four-step sequence of chemical operations.

Eine Synthese des β‐Sinensals

Stereoselective synthesis of .alpha.-sinensal

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