Substituent effects on the regioselectivity of carbon-hydrogen insertion arising during stereospecific intramolecular cyclization of 7-norcaranylidenes

Rearrangements of 1-cyclohexenylmethylenes and their relevance to the mechanism of the phenylcarbene rearrangement

“…As shown in Scheme IV below, a <r-mechanism for the rearrangement of (2-methyl-l-cyclohexenyl)methylene ( 27) is expected to lead to stable products different from those originating from intramolecular ir-attack. The former process is expected to lead to the isolation of 1-vinylcyclohexene (28) or to dimers of the allene 1-methyl-1,2cycloheptadiene (29), while the latter rearrangement is expected to produce l-methyl-l,3-cycloheptadiene (30) and its isomers 31-33 that result from facile 1,5-hydrogen shifts.14 The price paid for the presence of the methyl group was an additional reaction channel for (2-methyll-cyclohexenyl)methylene ( 27), formation of a cyclobutene derivative 34, expected to undergo ring opening to 1,2dimethylenecyclohexane (35). A similar ring opening has been observed for benzocyclobutene.18-16 (15) McMahon, R. J.; Chapman, 0.…”

“…When the liberated diazo compound 36 was evaporated through the pyrolysis hot zone at 500 °C, the products obtained consisted entirely of hydrocarbons, with a quantitative yield of C8HJ2 isomers. Of these, 24% consisted of 1,2-dimethylenecyclohexane (35), resulting from intramolecular attack of the (2-methyl-l-cyclohexenyl)methylene (27) carbene center on the methyl group. All the other products were isomeric methyl-1,3-cycloheptadienes 30-33, presumably resulting from initial intramolecular x--attack by the carbene center.…”

Silver(I) catalyzed rearrangements of strained .sigma. bonds. 39. Twofold cyclopropylidene carbon-hydrogen insertion as a route to hexacyclic bis(bicyclo[1.1.0]butanes) and their silver(I) ion promoted rearrangement. A direct synthesis of heptalene from naphthalene

“…Preparative VPC purification (10 ft X 0.25 in. glass SE-30, 135 °C) yielded benzocycloheptatriene (12): zw(film) 3020, 1490, and 1455 cm-'; NMR ( , CDC13-CC14) 7.31-6.99 (m, 4 ), 6.60-5.66 (m, 4 H), and 3.02 (d, J = 6.5 Hz, 2 H). This spectrum completely matched that of authentic material.…”

“…A regiocontrolled approach to the singlefold ring expansion of bicyclic olefins and dienes was described in the preceding to the very high selectivity of cyclopropylidenes in Ca-H insertion reactions. This discrimination appears in turn to be dictated by proximity factors and Ca-H bond nucleophilicities.5- 7 In conjunction with studies directed toward the rapid elaboration of medium-ring nonbenzenoid compounds of which heptalene is prototypical, we investigated the possibility of achieving twofold "naked" carbon atom insertions along the lines outlined in eq 4. Although the intended transformations require the intervention of exceedingly strained bisfbicyclo[l .1.0]butanes), we have discovered that such reactive molecules can be produced in good yield and readily handled.…”

Carbon atom insertion bicycloannulation: total syntheses of ishwarane and ishwarone

“…2: 1 ratio) in its 'H nmr spectrum indicated that both of the components had resulted from ring C-H insertion rather than methyl C-H insertion. The third product, however, which was produced in 28% yield, lacked a singlet in its 'H nmr spectrum, as expected for methyl insertion, and this compound was therefore assigned the structure of the desired product, norishwarane (20), possessing the complete ring system of ishwarane itself (1) but divested of the three methyl groups of the natural product.I8 As in the case of the Paquette study (30), mass balance considerations led us to tentatively propose that while the two ring C-H insertion products were derived only from the undesired a dibromocarbene adduct (concave attack on octalin 18), norishwarane (20) was the exclusive product from intramolecular insertion of cyclopropylidene (21) (corresponding to 8). These conclusions, on the other hand, would appear to imply that the preferred attack of dibromocarbene on octalin 18 is from the (presumably more hindered) concave face of the olefin, a seemingly untenable inference.…”