Diazomethane fulvenes

We predicted that electron-rich 1,3-dipoles in addition to diazomethane, such as nitrile ylides, would react in this fashion as well, and in 1978, Padwa and Nobs reported just such a reaction, shown in the second equation in Fig. 30. This reaction also gives some [4 + 2] adduct, in which the most nucleophilic terminus of the dipole has added to the 6-position of the fulvene. We have also found that electron-rich dienamines add to fulvenes in high yield (third equation of Fig. 30)85 These results... 

By contrast, if the important frontier orbital in a cycloaddition is the LUMO of the fulvene, and if the fulvene is to react as n2 or n6 component, it will now react as a ic6 component, because the largest coefficients are on C-2 and C-6. Thus with diazomethane, the LU (fulvene)/HO (diazomethane) interaction is probably closer in energy than the HO(fulvene)/LU(diazomethane) interaction (Fig. 4-72), and the adduct actually obtained (374)298 is the one expected from these considerations. Although reaction with a simple diene ought also to be dominated by the LU.(fulvene)/HO(diene) interaction (Fig. 4-72), nevertheless the observed294 product (376) from the reaction of dimethyl-fulvene (375) with cyclopentadiene has the fulvene acting as a n2 component rather than... 

Fig. 4-72 Frontier orbital interactions for fulvene, diazomethane and butadiene...

Further general route to 2-alkyl-2-butenolactones via the retro Diels-Alder reaction was developed, Fig. 5. [23], Hydrolysis of a known lactone (15), subsequent esterification with diazomethane, and treatment with dihydropyran afforded a stereoisomeric mixture of pyranyl ether. Alkylation of the pyranyl ether with various alkyl halide yielded alkylated products (16). The retro Diels-Alder reaction of 16 was performed by heating at 200-280 °C in a sealed tube to give 2-alkyl-2-butenolactones (17). The utility of the butenolactones was demonstrated by the synthesis of hinokinin (18) and dehydrolappaol A dimethyl ether (19). Similarly rather mild, simple synthesis of a-methylene-y-alkylbutyrolactones was deviced using dimethyl-fulvene as a protective group for the double bond, Fig. 6. [24]. The... 

Reactions of simple fulvenes with dienophiles commonly take place at C(2) and C(5) and those with dienes at C(2) and C(3), i.e. the latter proceed by a [2 + 4] rather than a [6 + 4] cycloaddition. This, and other features of cycloaddition reactions involving fulvenes can be nicely explained in terms of frontier orbital theory [234,235]. In some reactions fulvenes may participate as 6ir rather than 27t components, for example with diazomethane ... 

A pioneering study on [6-f4] reactions of diazomethane to dimethylfulvene was reported by Houk [54]. Other advances include the double [6+4] cycloaddition of tropone to dimethylfulvene [55], intramolecular [6+4]cycloadditions of fulvenes [56], selective intramolecular [6+4]cycloadditions of aminodienylfulvenes [57], and the [6+4] cycloadditions of diethylaminobutadiene to fulvenes for the synthesis of azulenes [58]. 

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