stable.['] The reason for this behavior is not clear. We hope to throw more light on the subject by building the new nucleosidephosphonates into oligonucleotides and studying their behavior toward duplex formation. As UV and CD measurements on many diastereomerically pure methylphosphonate dimers show, the bases of the Rp dimer occur in the stacked form, whereas the extended form prevails for the Sp isomer.['01 In the Sp configuration of the phosphodiester linkage, the substituent at the P atom is in a pseudoaxial position and thus in the vicinity of the nucleoside bases. Since this is the clearly preferred isomer in the synthesis presented here, the possibility exists that the structure of the molecule can be intentionally changed by a suitable choice of substituents. Now, further influence of either a steric, electronic, or covalent nature opens a new field for molecular modeling a t D N A molecules.The preferential formation of one isomer is in accord with our concept of the reaction mechanism. The diastereomeric selection takes place at the reaction of the monoester with the second nucleoside; we assume that it is a S,2(P) mechanism. The two approaches from which the attack can be initiated are blocked to different extents by the trityl protecting group on one side and the substituent at the phosphorus on the other. One approach is thereby energetically favored.["] If the substituent at the phosphorus atom is small, the attack is predominantly from this side and affords the Rp configurated product. However, if the substituent at the P atom is bulky, the attack from the side of the trityl group is more favorable, and the Sp isomer forms preferentially. In this case the yield decreases, since the space around the phosphorus atom in the monoester is already severely congested.Even the use of a chiral substituent, here (S)-( +)-2-methylbutyl, does not lead to a further increase in the diastereomeric ratio. Phosphorusamidites are also easily accessible as building blocks for solid-state synthesis via the monoester step; however, no statement about stereoselectivities and yields is yet possible. Experimental Procedure 3:A solution of ZnCI, (0.1 mol) in ether was added dropwise under argon at 0 "C to the Grignard compound l(O.1 mol) dissolved in ether (300 mL). A gray precipitate formed. The suspension was stirred for 15 min before it was transferred to an addition funnel and added dropwise to a boiling solution of PCI, (0.3 mol) and ether (SO mL). The mixture was stirred for a further 1 h under retlux, cooled to room temperature, and filtered by suction. and the residue washed with ether. The filtrate was evaporated to dryness, and the recovered solid fractionated in a stream of argon. "P NMR (121.5 MHz, CDCI,, 295 K, 85 "10 H,PO, external): benzyldichlorophosphane: 6 = 179.3; dichloroisopropylphosphane: 6 = 199.8; dichloro-(S)-( +)-2-methylbutylphosphane: 6 =

Abstract:The synthesis of the first fullerene cryptate 7 with a sodium ion bound to a benzo[2.2.2]cryptand covalently attached to a methanofullerene[60] is described. The amphiphilic properties of 7 as well as of a variety of other covalent fullerene derivatives with polar functional groups and the ability of these compounds to form Langmuir monolayers at the air-water interface were investigated C,, and methanofullerenes, four of which are fullerene C-glycosides. The films at the water surface were characterized by their surface pressure versus molecular area isotherms, compression and expansion in a systematic study. Among these S l o d g C t t~derivatives are Diels-Alder adducts of

Dedicated to Duilio Arigoni on the occasion of his 65th birthday (1.X.93)In the context of the hypothesis postulating a heterolytic cleavage of a C-N bond during thermolysis of alkoxydiazirines (Scheme I ) , we report the preparation of the diazirines4,5,7, and 8, the kinetic parameters for the thermolysis in MeOH of the diazirines 1 and 4-9, and the products of their thermolysis in an aprotic environment. The diazirines 4,5,7, and 8 (Schemes 2-5) were prepared from the known hemiacetals 10,19,34 (prepared from 31 in an improved way), and 42 according to an established method. The oximes 11,20,35, and 43 were obtained from the corresponding hemiacetals as (E/Z)-mixtures; 43 was formed together wlth the cyclic hydroxylamine 44. Oxidation of 11,35, and 43 (N-chlorosuccinimide/l,8-diazabicyclo[5.4.0]undec-7-ene (NCS/DBU) or NaIO,) gave good yields of the (Z)-hydroximolactones 12, 36, and 45, while the oxime 20 led to a mixture of the (E)-and (2)-hydroximolactones 21 and 22, which adopt different conformations. Their configuration was assigned, inter alia, by a comparison with the enol ethers 28 and 29, which were obtained, together with 30, from the reaction of the diazirine 5 with benzaldehyde and PBu,. Treatment of the hydroximolactone 0-sulfonates 13,23,37, and 46 with NH,/MeOH afforded the diaziridines 15,25,38, and 47 in good yields, while the (E)-sulfonate 24 decomposed readily. Oxidation of the diaziridines gave 4, 5, 7, and 8, respectively. Thermolysis of the diazirines 1 and 4-9 in MeOH yielded the anomeric methyl glycosides 50/51,16/17,26/27,52/53,39/40,48/49, and 54/55, respectively. A comparison of the kinetic data of the thermolysis at four different temperatures shows the importance of conformational and electronic factors and is compatible with the hypothesis of a heterolytic cleavage of a C-N bond. An early transition state is evidenced by the absence of torsional strain by an annulated 1,3-dioxane ring. Thermolysis of 1 in MeCN at 23" led mostly to the diastereoisoineric (Z,Z)-, (E,E)-, and (E,Z)-lactone azines 56, 57, and 58 (Scheme 6), which convert to 56 under mild conditions, and to 59 (3%). The benzyloxyglucal59 was obtained in higher yields (IS%), together with 44% of 5658, by thermolysis of solid 1. Similarly, thermolysis at higher temperatures of4 in toluene, THF, or dioxane and of 9 in CH2C12 or THF yielded the (Z,Z)-lactone azines 60 and 61, respectively, the latter being accompanied by the dihydro-oxazole 62.Introduction. -Diazirines [I] are important precursors of carbenes, and the mechanism of their thermolysis attracted considerable attention, which focused on the concertedness of the cleavage of the two C-N bonds and the homo-or heterolytic nature of the bond breaking [2-71. The mechanism and the kinetics of the thermolysis of (a1koxy)alkyldiazirines (see [8] and earlier papers of the series [9-131) have not been studied, but we hypothesized that thermolysis of 1-azisugars, such as 1, i.e. cyclic (alkoxy)alkyldiazirines, is initiated by heterolysis of one of the C( 1)-N bonds, accord-

No abstract

Thermolysis of the glycosylidene-derived 0 -benzylated diazirine 1 in the presence of N-phenylmaleimide (2), acrylonitrile (3), dimethyl fumarate (4), or dimethyl maleate (5) led in good yields to mixtures of the spirocyclopropanes 6/7, S l l , 12/13, and 12/13/16/17. The diastereoselectivity depends upon the alkene. The cycloaddition of 1 to 5 is not diastereospecific, in keeping with previous results. Deprotection of 12, 13, 16, and 17 yielded the tetrols 14, 15, 18, and 19, respectively.