Formation of gamma-lactams and lactones by radical cyclizations, homolytic aromatic alkylations, and preparation of levoglucosenone and its chiral derivatives.

摘要

Radical cyclization methodology has been explored for the formation of functionalized gamma-lactams and gamma-lactones in the addition of PhSO 2Br, under photolysis, to diene amides, or diene and enyne esters, respectively.;With N-allyl acrylamides CH2=CH2C(O)NRCH 2CH=CH2, only Calpha→Cbeta cyclization is observed where PhSO2· adds only to the acrylic C=C bond and then the adduct radical intramolecularly cyclizes by adding into the allyl C=C bond by a 5-exo mode. This cyclization shows trans selectivity and its chemoselectivity is confirmed by competition experiments.;The formation of gamma-lactones in the addition of PhSO2Br to allyl acrylates CH2=CHC(O)OCR1R2CH=CH 2 can be observed with trans selectivity when R1 and R2 are alkyl groups. The introduction of trace amounts of pyridine into the reactions can inhibit the acid-catalyzed hydrolysis and dehydration of the corresponding esters and therefore increase the yields of lactones.;Homolytic base-promoted aromatic alkylations can be observed with alkyl halides, (Bu3Sn)2, and DABCO in C6H 6 at 60°C. These results suggest that base-promoted homolytic aromatic substitutions may be a rather general process for aromatic compounds with electron-withdrawing substituents.;A convenient procedure for the preparation of levoglucosenone from cellulose has been investigated. Cellulose and H3PO4 are added to a vegetable oil, such as soybean oil, and the mixture is heated to 270--310°C under reduced pressure (20-30 mm Hg); within seconds levoglucosenone, water, and charcoal begin to form, and the water and the levoglucosenone are distilled from the mixture and condensed. Changes in the kind of vegetable oil and other aspects of the procedure have been explored. The yield of levoglucosenone is in the range of 5--10 wt% depending on the vegetable oil and heating rate, and its purity was ca 70 wt%. Preparation of several chiral derivatives of levoglucosenone have been investigated. (Abstract shortened by UMI.).