Polycyclic adduct

Strong acids or superacid systems generate stable fluorinated carbocations [40, 42] Treatment of tetrafluorobenzbarrelene with arenesulfonyl chlorides in nitro-methane-lithium perchlorate yields a crystalline salt with a rearranged benzo barrelene skeleton [43] Ionization of polycyclic adducts of difluorocarbene and derivatives of bornadiene with antimony pentafluonde in fluorosulfonyl chloride yields stable cations [44, 45]... 

Reactions of cyclopentyne with alkenes gives [2+2] cycloadduct with complete retention of stereochemistry (Scheme 24) [120], Laird and Gilbert observed the expected [2+2] cycloadduct along with the polycyclic adduct in the reaction of norbomyne with 2,3-dihydropyran (Scheme 24) [121], and located a cyclopropyl-carbene intermediate [122],... 

Further work by Trost established the involvement of metallacarbenoid species.292,293 A dimer product 307, incorporating a cyclopropyl group, was observed in the reaction of 304 in the presence of the highly electron-deficient palladole catalyst 305 (Scheme 78). This transformation is the signature of an intermediate of type 306. This chemistry could be rendered useful by playing with other unsaturated bonds as the carbene acceptor, and a variety of polycyclic adducts such as 308 could be synthesized. 

The mesoionic compound 86 corresponds to a thioisomiinchnone (61) and was generated by the carbenoid strategy approach. This dipole reacts with A(-phenyl-maleinimide to give the polycyclic adduct 87 (144) (Scheme 5.31). This method. 

Intramolecular [3- -2]-cycloadditions of thiocarbonyl ylides with nonactivated acetylenes have also been described. Most representative examples involved the use of mesoionic substrates. The initially formed polycyclic adducts of type 110 undergo spontaneous elimination of phenyl isocyanate (24,62,151). A typical example leading to compound 111 is shown in Scheme 5.40. 

The tandem double intramolecular 4 + 3/3 + 2-cycloaddition of the nitroalkene (10) produced the nitroso acetal (11) in 77% yield. Further functional group manipulations allowed for the conversion to the partial core (12) of the complex polycyclic alkaloid daphnilactone B in high yield (Scheme 3).6 The tandem intramolecular 4 + 2/3 + 2-cycloaddition cascade of 1,3,4-oxadiazoles (13) to polycyclic adducts (14) was investigated by considering the tethered initiating dienophile, the tethered dipolarophile, the 1,3,4-oxadiazole C(2) and C(5) substituents, the tether lengths and sites, and the central heterocycle (Scheme 4).7... 

Benzo[7]thiete 41 reacts in the ortho-qumoiA isomer 41 with cyclic trithiocarbonates such as l,3-dithiolane-2-thione, (ethylene trithiocarbonate), l,3-dithiole-2-thiones, and adamantanethione <1997LA1603>. In boiling toluene, 1,3 dithiolane and dithiole derivatives formed the spiro compound 42 and 43 in good yield. The related l,3-dithiole-2-thiones reacted chemoselectively at the C=S double bond. The use of adamantanethione yielded the polycyclic adduct 44 in a smooth and quantitative reaction (Scheme 3). 

An interesting example of an intramolecular 1,3-dipolar cycloaddition of an isomunchnone with an unactivated alkene to produce a complex polycyclic compound in one step has been reported <89TL4077 89CB1081>. The isomunchnones derived from the Rh2(OAc)4 catalyzed reaction of acyclic diazoimides 92-96 were found to undergo facile cycloaddition onto the tethered it-bond to provide polycyclic adducts 97-101. A notable feature of this cycloaddition is that only one diastereomer is formed. The relative... 

Cyclopentadienone equivalents, such as 4-acetoxy-2-cyclopenten-l-one, below, may serve as conjunctive reagents for tandem Diels-Alder reactions providing polycyclic adducts." ... 

Several iodonium- and bis(iodonium) norbomadienes and other polycyclic adducts have been synthesized by [2-1-4] cycloaddition reactions of alkynyliodonium triflates with cyclic 1,3-dienes [458,460-464]. In particular, the bis-iodonium acetylene 331 undergoes Diels-Alder reactions with cyclopentadiene 329, furan... 

The formation of 5-membered ring carbonyl ylides from a 5-keto fimc-tionality was shown to undergo the intramolecular [3+2]-cycloaddition with alkenes or alkynes. An illustrative example [79] is the reaction of acyclic diazo ketone 71 with a catalytic quantity of rhodiiun(ll) acetate at room temperature to afford the polycyclic adduct 72 in 50% yield with complete diastereoselectivity (Scheme 21). This example shows that the intramolecular cycloadditions of 5-membered ring carbonyl ylide can take place across the unactivated 1-hexenyl zr-bond. 

Octamethylbicyclo[4,2,0]octa-2,4,7-triene has been prepared from octamethyl-cyclo-octatetraene via its dimethyl azocarboxylate adduct. The rearrangement of octamethylbicyclo[4,2,0]octa-2,4,7-triene back to the monocyclic octamethylcyclo-octatetraene was studied and the Diels-Alder adducts with TCNE and maleic anhydride were prepared. Cyclo-octatetraene and vinylene carbonate react at 180°C to give the polycyclic adduct (150 50%) mechanisms for this reaction were discussed. 

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