Methylenation products

Upon subsequent addition of protons the methylene product 2 is formed. 

In the presence of dibutyl telluride, iodomethyl triphenylphosphonium iodide reacts with aldehydes, in accordance with a Wittig-type olefmation, giving methylenation products. ... 

The route used to prepare the unsaturated 2 methyl androgen stenbolone provides yet a further illustration of the propensity for the formation of enolates at the 2 position. Thus reaction of dihydrotestosterone acetate (41-1) with formaldehyde and dimethylamine gives the Mannich product (41-2). Hydrogenolysis of that product gives the 2 methyl derivative (41-3) the relatively elevated temperature used for this last reaction suggests that the reaction may proceed via the methylene product... 

Tebbe reagent as well as Zn-CH2X2-TiCl4 did not give satisfactory results. However, the combination of 3 and /9-TiCl3 gave fully methylenated products without racemization. 

Duncan and Cvetanovic27 studied the reaction with isobutene of methylene generated by the mercury photosensitized decomposition of CH2CO, which is believed to produce triplet methylene. Product ratios reached high-pressure limiting ratios at 200 mm. The observed yield of... 

High vacuum pyrolysis of (2) gives mainly the 16-methyl-A16-steroid (3) besides a small quantity of the 16a, 17a-methylene product (4).188,189... 

The corresponding Wittig reagent, CHj PPhj, reacts smoothly with both aldehydes and ketones to give methylenated products In high yield but with one subtle limitation. The problem cannot be detected with aldehydes because they react rapidly even at temperatures as low as -78°C, but ketones react more slowly, and an adjacent enolizable chiral center can be epimerized as a result of competitive reversible enolization. This limitation of the Wittig... 

Dibutyl telluride 59 reacts with iodomethyl triphenylphosphonium iodide to give triphenylmethylidene phosphor-ane, which reacts with aldehydes leading to the methylenation products in good yields.119 The same reagent 59 also assists the reaction of dibromomalonates 60 with aldehydes and activated olefins affording alkylidene malonates 61 and cyclopropanes 62 derivatives, respectively (Scheme 30). 

The products can be hydrodesilylated by reaction with HCl in CH,OH or with CsF or KF in aqueous DMSO or DMF. The former reaction occurs with almost complete shift of the bond to give exo-methylene products. The latter results in endo- and exo-methylene compounds in the ratio —85 15. These reactions provide attractive routes to various terpenes. 

These a metalated organosilanes react with carbonyl compounds to give methylenated products. 

With 1,4-diketones the distribution of the reduction products is dependent on the stereochemical situation of the two carbonyl functions. In acyclic derivatives, with no stereochemical interaction between the two carbonyl functions, the ketone groups are independently reduced to give methylene products in the usual manner. On the other hand, cyclic 1,4-diketones react differently. For example, cyclohexane-1,4-dione (22) suffers ring opening to give hexane-2,5-dione and hex-5-en-2-one derivatives, and products of further reduction are also detectable (equation 11). A 1,4-diketone (23) in which the two carbonyls are stereochemically close, gave the diketone (24) under relatively mild conditions (Zn/AcOH, 25 C), formed by the same C—C bond cleavage as seen in cyclohexane-1,4-dione. Under Clemmensen conditions this derivative was then converted to cyclobutane-1,4-diol (25 equation 12) in 98% yield, which is closely related to the aforementioned cyclopropanediol intermediate. ... 

Similarly reduction of o- or p-hydroxy-substituted aryl ketones with NaBHa in refluxing aqueous NaOH solution gives rise to an intermediate methylene quinone (26), which is further reduced to the desired methylene product (equation 14). When the hydroxy group is situated only at the meta position, there is no possibility to make such a methylene quinone intermediate, and the corresponding benzyl alcohol (27) is formed (equation 15). 

Early work by Papa et al. indicated that reduction of carbonyl compounds with Raney nickel in alkaline solution gave the corresponding hydrocarbon or alcohol products, and formation of the hydrocarbon was only feasible in the case of aromatic carbonyl compounds at 80-90 C. Mitchell et al. reported an improved method under neutral conditions using W-7 Raney nickel in 50% aqueous ethanol, aryl aldehydes, alkyl aryl and diaryl ketones can be reduced to the methylene products in high yields. Aromatic substituents such as nitro, cyano and halogen also suffer reduction under these conditions. 

The Wharton reaction has also been applied to the conversion of exocyclic a,p-epoxy ketones to the corresponding exocyclic hydroxy methylene products (Scheme 17). Similar conditions transform exocyclic methyl ketones into the exocyclic ethylidene derivative (Scheme 18). Not unexpectedly, the (Z)-alkene is isolated in only slightly higher yields than the ( )-isomer. 

Succinimides (62) react to form the contesponding mono- (alkyl substituents are present in the a-position, a high degree of regioselectivity is observed for reaction at the less-hindered carbon. All of the diaddition compounds have the potential of isomerization to the pyrrole (65 Scheme 16). Piperidinediones (66), however, react predominantly by the enolization pathway to give (67 equation 15). ... 

Methylenation of aldehydes and ketones. A reagent prepared in CH2CI2 from CH2I2, Zn, and TiCh is considerably more reactive than one prepared from CH2Br2, Zn, and TiCh (8, 339,11, 337,12, 322). Moreover, it affords less of the coupled products. This new reagent does not react with esters. It is particularly useful for methylenation of easily enolizable ketones, for which the Wittig reagent is not useful. The isolated yields of some methylenated products are shown. 

Ring-opening polymerization of methylenecyclopropane in the presence of 4-type precatalyst proceeds to yield cxo-methylene products in low yield [87] 4-type precatalysts do not polymerize oxiranes. 

In hindered or strained systems the yields are more variable. Thus, the yield of methylene product from 1-chloro-l-methyl-2,2-diphenylcyclopropane was only 39%. ° In a series of methylenecyclopropanes containing a bicyclic system with aryl bridgehead substituents, the yields in some cases were very poor (Table 1). In the absence of such substituents, however, the yields are generally very good. Thus, a 78% yield of pure 7-methylenebicyclo[4.1.0]heptane (13, n = 2) and a 85% yield of pure c/5-9-methylenebicyclo[6.1.0]nonane (13, n = 6) were obtained from the 1-chloro-l-methylcyclopropanes 12 derived from cyclohexene and (Z)-cyclo-octene, respectively. ... 

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