Stereoselektive Synthese von 3‐substituierten Cyclobutanolen und Folgeprodukten

Abstract

Stereoselective Synthesis of 3-Substituted Cyclobutanols and Products Derived TherefromDie Reduktion der Cyclobutanone zu den Cyclobutanolen 3 und 4 wurde rnit verschiedenen Reduktionsmitteln erprobt (Tab. 1). Wie zu erwarten, liefert das sterisch anspruchsvolle Lithium-tri-tert-butoxyaluminiumhydrid die hochste cis-Stereoselektivitat von 95 bis fast 100%. Somit sind die cis-Verbindungen 3 gut zuganglich. Dagegen wurde keine einfache Methode zur reduktiven Darstellung der trans-Verbindungen 4 aufgefunden. Selbst die Lewis-sauren Reduktionsmittel wie DIBAH liefern zwar erhohte, aber praparativ nicht ausreichende trans-Selektivitaten.Ein anderer potentieller Weg zu den Verbindungen 4 beginnt rnit der Dichlorketen-Addition an Alkine. So lassen sich z.B. 5a,b['03111 rnit ZdTMEDNEisessig zu 6a,b reduzieren" ' 1. Die erhoffte ein-oder zweistufige Reduktion bzw.

New Ring Expansion of Cyclobutanones: Synthesis of Pyrrolinones, ­Pyrrolidines and Pyrroles

“…Ring opening of 3-butyl-2,2-dichlorocyclobutanone 14 (18) with isopropylamine yielded butanamide 19 in quantitative yield. Reaction of 19 with sodium methoxide resulted in enol ether 20 which could be cyclized by treatment with aqueous HCl.…”

“…To expand the scope of the ring expansion, effords were done to perform the reaction sequence with alkylcyclobutanones (Scheme 6). Ring opening of 3-butyl-2,2dichlorocyclobutanone 14 (18) with isopropylamine yielded butanamide 19 in quantitative yield. Reaction of 19 with sodium methoxide resulted in enol ether 20 which could be cyclized by treatment with aqueous HCl.…”

Friedel–Crafts Alkylation of Aromatics by TiCl4-Promoted Ring Cleavage of 3-Arylcyclobutanones

“…All reactions were carried out under N 2 in dried glassware with magnetic stirring. Cyclobutanones 1a, 15 1dg, 16 and 1h 17 were prepared by reported procedures.…”

New Synthesis of Semisquaric Acid Derivatives via Chlorinated N-(Cyclobutylidene)amines

“…Readily available 3-substituted 2,2-dichlorocyclobutanones 10 26 were dehalogenated with zinc in acetic acid prior to the conversion to imines 12 because a direct imination of dichlorinated cyclobutanones 10 was not successful and resulted in complex reaction mixtures. In contrast, dehalogenated cyclobutanones 11 were easily iminated using titanium(IV) chloride as an activating and dehydrating agent, resulting in new imines 12 (Scheme ). The reaction of these new compounds with 4.5 equiv of NCS in refluxing CCl 4 for 30 min resulted in a 2,2,4,4-tetrachlorination toward novel imines 13 in high yields.…”