Propellanes, heterocyclic

The cycloaddition reaction of heterocyclic propellanes 99 (X = O and S) with iV-phenyltriazolinedione (NN) (Fig. 16) affords the anti adduct with respect to the bridge [166-168]. Replacement of the a-CH groups by carbonyls (that is 100),... 

I should like to attempt to explain why a starting material that may apparently afford a propellane and/or a dispiran sometimes gives one or another, apparently not a mixture of both. There does not appear to be a denominator common for all the cases to be discussed but perhaps discussion of cases pertaining both to carbo-cyclic and heterocyclic compounds may cast some light on the problem there need not be a unique reason for the behavior in the two series. 

To emphasize this statement I should like to begin with a heterocyclic case which provides an outlet for the molecule s behavior that leads to neither propellane or spiran albeit, on paper, both of these types might be expected to form. In Mulheim/Ruhr the following reaction was studied ... 

Let us now discuss heterocyclic propellanes and dispirans. 8,1 l-Dioxa[4.3.3]propell-3-ene 34 was prepared (in 73% yield) by heating the tetrol 33 with KHS04 at 190-200 °C4e). This was accompanied by the bicyclic ether 35 (10% yield) but no... 

There are many more syntheses of heterocyclic propellanes from 1,1,2,2-substituted carbocyclic starting materials. The tetrol discussed above, when treated with KHS04 at 170-190 °C affords the dioxa[3.3.2]propellane shown no isomeric spiran is mentioned. Although the yield is only 50% perhaps some dispiran is hiding in the brauner Ruckstand from which the propellane diether is either crystallized at low... 

To the Buchta heterocycles the higher homologs must also be added. The cyclopentane-1,1,2,2-substituted tetrol 54 was cyclized, in this case heated rapidly with H2S04 at 160-170°, to give the dioxa[3.3.3]propellane 55 in 74 % yield, no dispiran by-product being mentioned here either13). 

Many reducing agents are capable of severing a carbon-halogen bond. Cathodic cleavage provides perhaps the most versatile method, and has been put to excellent use. The electrochemical variation of the Wurtz reaction constitutes a powerful method for the construction of a variety of rings, particularly strained systems. Dramatic examples are provided by the assembly of bicyclobutane (308) [89], bicyclohexene (310) [90-92], [2.2.2]propellane (312) [93], spiropentane (316) [94], j -lactams 318 [95], and a variety of small-ring heterocycles (320) [96,97]. 

If R1 and R2 are a tri- or tetra-methylene bridge then the products (127) are heterocyclic propellanes (78CI(L)95>. Photolysis of the sulfone (128) eliminates sulfur dioxide to give a 47r-electron system which can be trapped by N- phenylmaleimide (Scheme 41) (78JOC3374). 

Addition to six-membered oxygen heterocycles is also common. The photocycloaddition of 5,7-dimethoxycoumarin to tetramethylethylene has been described,269 and 4-hydroxycoumarin (326) undergoes facile addition to cyclohexene on direct irradiation to give the cyclobutane (327)270 analogous additions to a variety of other alkenes have been reported, and the cycloaddition of 4-methoxycoumarin to 2-methylpropene has been employed in a synthesis of l,2-dihydrocyclobuta[c]coumarin.271 Photoaddition of the 1,2-bisenol lactone (328) to tran.s-stilbene yields propellane (329),272 and [ 2 + 2] cycloaddition is observed along with other competing photoreactions on irradiation of chromone in the presence of alkenes.273... 

Centropolyindanes constitute a complete family of arylaliphatic polycyclic hydrocarbons containing several indane units. Mutual fusion of the five-membered rings leads to three-dimensional, carbon-rich molecular frameworks bearing a central carbon atom, such as benzo-annelated [3.3.3]propellanes, triquinacenes, and [5.5.5.6]- and [5.5.5.5]fenestranes. In this review, the structural concept of centropolyindanes is contrasted to other fused indane hydrocarbons. Besides the syntheses of the parent centropolyindanes and recently described related indane hydrocarbons, the preparation of a large variety of bridgehead and arene substituted centropolyindanes is presented including strained, heterocyclic, and centrohexacyclic derivatives. In appropriate cases, the particular reactivity and some structural features of these unusual, sterically rigid polycyclic compounds are pointed out. 

Miscellaneous Reactions of Phosphines.- Theoretical treatments have appeared of a number of strained heterocyclic phosphine systems, notably phospha[3]radiaIene (148), triphospha[l, 1, l]propellane (149), and the tetraphosphacubane system (150). The reactivity of tetrakis-r-butyltetraphosphacubane has been studied in superacid media, with respect to protonation, alkylation, and alkynylation. Stable monophosphonium ions have been characterised. ... 

Several heterocyclic [3.2.1]propellanes are available through addition of furans and 1,2,3-trimethylisoindole (155) to 122. Furan, for example, yields 156 . ... 

This relative stability of cyclopropanone-zwitterion in five-membered rings can be generalized, as a similar behavior is found, for instance, in the Ram-berg-Backlund reaction of a-halogenated sulfones. (The mechanism of this reaction is known, and involves the formation of an episulfone heterocyclic analog of the cyclopropanone.) When this intermediate is formed in a strained system such as propellane 41, Paquette and coworkers suggest that it opens to a zwitterion in order to explain the formation of the substitution product 42. 

Alizadeh has disclosed a highly chemoselective heteroannulation protocol for the synthesis of polysnbstituted heterocyclic[3.3.3]propellane systems comprising dihydropynole and dihydrofuran rings (compounds 34 and 35) from the sequential four-component reaction in water at room temperature between ninhydrin, malo-nonitrile, primary amines and a fourth component chosen between dialkyl acetyl-enedicarboxylates or p-ketoesters [23] (Scheme 1.17). 

Keywords Ninhydrin, malononitrile, aryl isothiocyanates, primary aliphatic amines, ethanol, triethylamine, room temperature, one-pot multicomponent synthesis, thio-Michael and Knoevenagel reactions, sulfur-nitrogen heterocycles, oxathiaaza[3.3.3]-propellanes, che-moselectivity, regioselectivity... 

O-bridged 31, 616 cyclols 32, 421 S-heterocyclics 31,969 lactolides, bicyclic 31, 248 nitriles 31, 692 peroxides, cyclic 32, 120 propellanes 21, 746s31 32, 753 pyrrolo[2,l,5-cd]indolizines... 

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