Cyclopropanization of Methyl Carboxylates with Tebbe‐Type Reagents

Abstract

The methylenation reaction of methyl azulene-2-carboxylates (cf. Schemes I and 2 ) with Tebbe's or Takai's reagent is described. When the prescribed amount of Tukai's reagent is applied in a four-fold excess, the corresponding cyclopropyl methyl ethers are formed instead of the enol ethers (cf. Schemes 2 and 3 ) . Similarly, methyl benzoate and methyl 2-naphthoate yield, after treatment with Takai's reagent and hydrolysis, the corresponding cyclopropanols 18 and 19, respectively (Scheme 3 ) . The cyclopropyl methyl ether 4 or cyclopropanol5 rearrange, on acid catalysis, into the I-(azulen-2-yl)propan-l-one 20 (Scheme 4 ) whose reduction with Et,SiH in CF3COOH yields the 2-propylazulene 21.

Titanium reagents for the alkylidenation of carboxylic acid and carbonic acid derivatives

“…40 conditions, but when an excess of the reagent is used, cyclopropyl ethers 149 and 150 are produced in good yield (Scheme 80). 117 Methyl benzoate undergoes the same reaction, albeit in modest yield, but methyl phenylacetate does not. Enol ethers are not cyclopropanated under these conditions.…”

Synthesis of Benz[a]azulenes Substituted at the Benzo Ring

“…'H-NOE (CDCI,): 3.12 (Me-C(10))-8.66 (s, H-C(l)), 7.1 1 (s, H-C(9)); 2.84 (Me-C(6))-7.35 (s, H-C(5)), 7.12 (s, H-C(7)); 2.59 (Me-C(8))+7.12 (s, H-C(7)), 7.11 (s, H-C(9)); 1.86 The locants of the substituent are primed. (19), 152(33), 114 (13),91 (14),83(lI),82 (14),81 (13),77 (14),73 (17),71 (18),69 (17),68(11),59(9),57(35),56 (47), 55 (41), 54 (ll), 51 (17). 1.7.…”

“…[19]) to yield 0.585 g (92%) of pure (E)-9. Diethyl 1.2-Dihydro-6.8,lO-trimefhylbenz[ a]uzulene-2.3-dicarhoxylute (13). Compound (E,E)-11 (0.700 g, 0.705 mmol) was heated in p-cymene (20 ml) at 180" during 12 h. The solvent was distilled off in a Kugelrohr apparatus at 50°/12 mm.…”

“…We report here on first results of the application of this annelation concept to the synthesis of new benz[u Iazulenes. [13]), followed by hydrolysis of the formed enol ether (cf. Scheme 2).…”

A Metathesis-Based Approach to the Synthesis of Furans

“…It has also been shown that the use of excess Takai-Utimoto reagent can result in the cyclopropanation of aromatic esters. 21 While this unwanted product was observed in some cases, it could be minimized by careful optimization of the conditions, which allowed access to triaryl aromatic compounds in good overall yields (Table 1, entries 1 and 2).…”