Cyclopropanes with lead tetraacetate

Cyelobutanone has been prepared by (1) reaction of diazomethane with ketene,4 (2) treatment of methylenecyclobutane with performic acid, followed by cleavage of the resulting glycol with lead tetraacetate,s (3) ozonolysis of methylenecyclobutane, (4) epoxidation of methylene-cyclopropane followed by acid-catalyzed ring expansion,7 and (5) oxidative cleavage of cyclobutane trimethylene thioketal, which in turn is prepared from 2-(co-chloropropyl)-l,3-dithiane.8... 

The 2,3-dihydro-l//-pyrazole obtained from the reaction of hydrazine with an a-)8-unsaturated carbonyl compound will sometimes give a sufficient proportion of the 4,5-dihydro-3i/-pyrazole tautomer at equilibrium so that it is possible just to heat the 1//-tautomer to eliminate nitrogen and form a cyclopropane. In other cases, it is necessary to reduce the 1//-tautomer and oxidize back to the 3 -form. It is also possible to use the conversion of the H- to the 3//-tautomer to introduce substituents at C3 of the 4,5-dihydro-3//-pyrazole and hence into the cyclopropane. The reaction of 4-methylpent-3-en-2-one with hydrazine gave 2,2,4-trimethyl-2,3-dihydro-lH-pyrazole (1). Treatment with lead tetraacetate gave the 3-acetoxy derivative 2 and on thermolysis, l-acetoxy-l,2,2-trimethylcyclopropane (3). Alternatively, tosylation and reaction with methyllithium gave 3,3,5,5-tetramethyl-4,5-dihydro-3//-pyrazole (4) which on thermolysis or photolysis gave 1,1,2,2-tetramethylcyclopropane route to tetramethylcy-... 

Stereoisomeric ethyl 4,5-dimethylspiropentane-l-carboxylates 11 were prepared by copper-catalyzed addition of ethyl diazoacetate to cis- and tra .v-l,2-dimethyl-3-methylenecyclo-propane and by cyclopropanation of four isomeric ethyl 2-ethylidene-3-methylcyclopropane-l-carboxylates. The ethoxycarbonyl group was removed from the spiropentane system by saponification followed by treatment with lead tetraacetate, iodine and reaction with tributyltin hydride, both with irradiation. ... 

Organocopper reagents, 207 of cyclopropanes Dimethyl sulfoxide, 124 Lead tetraacetate, 155 of epoxides (see also Rearrangement reactions, Reduction reactions) with organocopper reagents... 

Cyclopropanation and Aziridination (Alkene Three-Membered Cycloadduct) - Cyclopropanation of various trans-N-enoyl derivatives using diazomethane with Pd(OAc)2 as catalyst affords cyclopropyl products with good C(a)-re -facial control (eq 8). Similarly, aziridination with N-aminophthalimide-lead tetraacetate affords N-phthalimidoaziridines with variable but generally good jr-face selectivity (33-95% de). ... 

The high reactivity of the Pb—O bond raises the question whether oxyplumbation is of importance in the often useful reactions of lead tetraacetate (40), as is commonly assumed. At least, oxyplumbation is postulated for the cleavage of the cyclopropane ring by Pb(OAc)4 212) as in the reaction of styrene with acetylacetone in the presence of Pb(OAc)4 119). 

A cyclopropane ring was also apparent in the pmr spectrum of (55). Oxidation of (55) with osmium tetroxide followed by lead tetraacetate gave a new y-lactone (57) (Fig. 23) with the same structure as (55) at C-7 through C-15. Inclusion of the cyclopropane ring completes the assignment of structure to (57), while consideration of the groups lost in the oxidation allows assignment of (55). 

Oxidation of trimethylsiloxycyclopropanes with AgBF4 results in the formation of 1,6-diketones [125], Lead(IV) tetraacetate, which is able to oxidize a cyclopropane ring [126], induces the fragmentation of both the a and b bonds of 229 in acetic acid to give the olefinic carboxylic acids 230 [127], (Scheme 91)... 

Cyclopropanation of dienes 90 or 94 with 3,3-dichlorodiazopropene (91b) or the parent diazo compound 91 a (X = h) in the presence of dirhodium tetraacetate leads to a mixture of the rearranged fused eyeloheptadienes 93 and 96 and the stable tra .v-l,2-divinylcyclopropanes 92 and 95. The trans- 1,2-divinyl derivatives can be transformed to the seven-meinbered ring by heating to 110 °C854. 

---