Synthesis and characterization of spiro[3.4]octa-5,7-diene

Abstract

When 0.25 mol of CF2Br213 (52.5 g, 22.8 ml) was added to a solution of 0.25 mol of Ph3P (65.5 g) in 450 ml of dry triglyme, a heavy precipitate of [Ph3P+CF2-Br]Br~quickly formed. The solution was stirred for 30 min under dry nitrogen followed by addition of 0.25 mol of Me2C=CHMe (17.5 g, 26.25 ml) and 1.0 mol of anhydrous KF (58.1 g). The solution was stirred vigorously for 24 hr and then flash distilled at ca. 3 mm.Fractionation of the distillate yielded 20.0 g of product (bp = 69-70°) which was 99 % pure by glpc analysis. The nmr showed a multiple! at 0.85-1.35 ppm and the 19F nmr consisted of two signals, 139.8 ppm (d of m) and 151.9 ppm (d of broad singlets) ( *, CFC13) with a doublet splitting of 153.6Hz. The mass spectrum was consistent with the assigned structure of the product, 1, 1-difluorotrimethylcyclopropane. The isolated yield was 67 %.The use of these phosphonium salts compares favorably with other precursors of difluorocarbene. In most cases, however, the availability of reagents, ease of scaling up the reaction, mild conditions of the reaction, and the ease of isolation of the products make this mode of carbene generation the method of choice.Related work in our laboratories indicates that other phosphonium salts may be useful carbene precursors.8 Details of these experiments will be presented in due course.

Synthesis of 7,7-dimethylnorbornadiene

“…The mixture was allowed to stand for 5 min, followed by hydrolysis and extraction with ether. The ethereal phase was washed with brine, dried over MgSCL, and concentrated (10 °C/100 torr) to give alcohol 10 (1.89 g, 93%), pure according to GLC (FFAP 15%/Chromosorb W, 3 m X 3 mm, 80 °C) and spectroscopic analysis: NMR (CCL, 100 MHz) ó 1.03 (s, 3 ), 1.13 (s, 3 ), 1.50 and 2.0 (ABX centered at ó 1.74, Ay = 14 Hz, = 5 Hz, Ax = 7 Hz, 2 H), 3.59 (s, 1 H, OH), 4.79 (m, 1 H), 5.63 (m, 2 H); IR (neat) 3320 s, 3040 m, 1622 w. 1050 s. 780 m cm"1: MS m/e 112 (M, 20), 97 (100), 69 (28), 57 (21), 55 (34), 43 (65), 41 (59), 39 (23).…”

Spirocyclization enhances the Diels–Alder reactivities of geminally substituted cyclopentadienes and 4H‐pyrazoles

“…As shown in Scheme 1, diMe-Cp does not dimerize even at temperatures as high as 200 C. [11,12] This recalcitrance is in contrast to cyclopentadiene (Cp), which readily dimerizes with a halflife of $28 h at 25 C. [13,14] The cyclobutanecyclopentadiene spirocycle, spiro [3.4]octa-5,7-diene (4-Cp), also readily dimerizes. [15][16][17] At 50 C, the rate constant suggests that the dimerization of 4-Cp occurs $220-fold faster than the dimerization of Cp. [15,18] The increased rate of dimerization observed in 4-Cp interests us because it suggests that spirocyclization enhances the Diels-Alder reactivity of 5-membered dienes.…”

“…[ 13,14 ] The cyclobutane–cyclopentadiene spirocycle, spiro[3.4]octa‐5,7‐diene (4‐Cp), also readily dimerizes. [ 15–17 ] At 50°C, the rate constant suggests that the dimerization of 4‐Cp occurs ~220‐fold faster than the dimerization of Cp. [ 15,18 ] The increased rate of dimerization observed in 4‐Cp interests us because it suggests that spirocyclization enhances the Diels–Alder reactivity of 5‐membered dienes.…”

Addition initiated ring closure: synthesis of substituted spiro[2.4]hepta-4,6-dienes via cyclopentadiene intermediates from fulvene precursors

“…These results are summarized for a variety of lithio nucleophiles in Table 1. The alternative cyclization to form the cyclobutane 4 requires an endo-tet ring opening which is disfavoured (18)(19)(20)(21), as is the spiro[3.4]octa-l,3-diene system itself (22)(23)(24). In a typical example, addition of methyllithium to the fulvene-epoxide 1 at -78°C in tetrahydrofuran followed by warming to P C afforded the spiro-alcohol 9 as the sole product after work-up and chromatography.…”