Homo-Favorskii rearrangement

Abstract

of 5 by benzophenone and acetone is attributed to eq 13, energy transfer to B to regenerate A. Since eq 13 simply increases the steady-state concentration of A and eq 8 and 12 have been included, operation of eq 13 can enhance the yield of 4 as well as that of 5.The observed results can be explained by assuming that A and B are tetramethylcyclobutadienes differing in multiplicity, one a singlet state and the other a triplet. Conversion of A to B, eq 10, could easily be assisted by long-lived radical species (02,-CCE, and other intermediates) or by heavy atoms in the solute. This could also explain the sensitivity of Gs to impurities present in the additives and those building up during the course of the irradiation. It is tempting to suggest that A is a triplet cyclobutadiene and B is a lower energy singlet. Theoretical calculations52 suggest that for free cyclobutadiene a "rectangular" singlet should lie 14-21 kcal/mol below a "square" triplet.Recent experimental evidence appears to indicate a rectangular singlet is the ground state of cyclobutadiene.53 Such an energy difference would explain a lack of quenching of A (and hence 5) by azulene ( « 31-39 kcal/mol)54 and other additives with higher triplet energies. Presumably lack of observed increases in G5 could be due to short lifetimes for triplets (52) M.

Cyclopropanol derivatives as intermediates for organochemical synthesis

“…The residual oil, 590 mg, was chromatographed on activity I alumina. Elution with hexane yielded 490 mg of dihydrojasmone (28), infrared and pmr spectrally identical with an authentic specimen; semicarbazone, mp, mmp 173-175°.…”

“…Dihydrojasmone (28). A solution of 10.1 g of «-enanthyl chloride in 100 ml of dry ether was added dropwise over a period of 3 hr to a solution of diazomethane (from 43.0 g of Ar-nitroso-Armethylurea) in 400 ml of ether at 0°.…”

“…Acid treatment of either carbinol 4b, prepared by the lithium aluminum hydride reduction of ketone 3b25 followed by Simmons-Smith reaction9•26 on alcohol 3c, or 4d, produced by a Fétizon oxidation27 of 4b followed by lithium aluminum hydride reduction of 4c, led to the bicyclic ketone 17.18,28 These transformations could serve as model reactions for the synthesis of the sesquiterpenes bourbonenes (18).29 Furthermore, they shed some light on the mechanism of the homo-Favorskii rearrangement. 28 A reaction in which -oxycyclopropylcarbinyl systems play an important role is the acid-catalyzed rearrangement of cyclobutanones.80 One manifestation thereof is the following transformation of a cyclobutanone intermediate on route to the sesquiterpene family of the copaenes and ylangenes into one on route to the bourbonenes (18). Treatment of bicyclic chloro ketone 1918 with formic acid yielded isomer 21a.…”

“…The following cases show the potential for ring scission among carboxylic esters.43 Treatment of 8c, lib, and lid with acid produced 24a, 24b, and 13f, respectively. Base hydrolysis of the diester 13f yielded , -dimethylsuccinic acid (13g).44 Finally, the following synthesis of dihydrojasmone (28) illustrates the utilization of an acyloxycyclopropane whose cationoid center is at the oxidation level of a ketone. 45 An interaction between l-diazo-2-octanone ( 25), isopropenyl acetate (26), and copper-bronze yielded a mixture of stereoisomeric cyclopropanes ( 27) whose treatment with base gave dihydrojasmone (28).46 (40) Contrastingly, a reaction of ethyl diazoacetate, 1,1-diethoxyethylene, and cuprous bromide or copper powder has been reported to yield the acyclic ester v [M. F. Dull and P. G. Abend, J. Amer.…”

Synthetic utilization of the imine moiety. 6. Intramolecular carbon alkylation of oxime anions. Stereospecific generation and rearrangement of nitrosocyclopropanes and nitrosocyclobutanes

“…Reaction of oxime 6 with a suspension of potassium ZerZ-butoxide in tetrahydrofuran did not afford isolable cyclopropyl nitroso compound 7. The sole kinetic reaction product was the ring-contracted syn8 oxime 8.6"8 apparently via a homodienyl [1,5]-hydrogen migration on intermediate 7.…”