Synthesis of 1,3-Substituted Cyclobutanes by Allenoate-Alkene [2 + 2] Cycloaddition

Abstract

A method for the [2 + 2] cycloaddition of terminal alkenes with allenoates is presented. This process allows for the rapid synthesis of 1,3-substituted cyclobutanes in high yield under simple and robust reaction conditions.

Two‐Step Procedure for the Synthesis of 1,2,3,4‐Tetrahydro‐quinolines

“…Delighted by the fact that the chloro-substituted substrates offer advantages in the initial hydroaminoalkylation reaction as well as in the subsequent Buchwald-Hartwig coupling, we used ortho-chlorostyrene (7) as the starting material for all further studies. To further investigate the scope of the hydroaminoalkylation of ortho-chlorostyrene (7) we performed corresponding reactions on a 2 mmol-scale with various functionalized secondary anilines (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24) in the presence of 10 mol-% of catalyst II (Table 3). During this study, it was first found that para-methoxy-N-methylaniline (12) and para-thiomethyl-N-methylaniline (14) deliver the corresponding products 25b and 27b in good yields of 61 % and 58 %, respectively.…”

“…The crude product was purified by flash chromatography (SiO 2 ). [15] A dried Schlenk flask was charged with methyltriphenylphosphonium bromide (42.87 g, 120.0 mmol), evacuated and backfilled with argon three times. Then the solid was suspended in Et 2 O (300 mL) and while vigorously stirring KOtBu (13.47 g, 120.0 mmol) was added.…”

Cycloadditions of Alkenylboronic Derivatives

“…Another example of thermal [2+2] cycloaddition included the Lewis acid catalyzed reaction of allene 72 with pina-col ester 73 giving cyclobutyl boronate 74 in 80% yield (Scheme 34). 76 Recently, photochemical [2+2] cycloaddition of maleimides and maleic anhydride 76 with alkenyl boropinacolates 75 was described by our group (Scheme 35). 77 In this case, the reaction was performed at a 1:1 ratio of the reagents using a 366 nm lamp irradiation and gave target products 77 in 49-93% yield.…”

Synthesis of organic liquid crystals containing selectively fluorinated cyclopropanes

“…The synthesis of the diastereoisomers of spiro LC candidates 11a and 11b also started from ketone 15 as illustrated in phosphine which was generated in situ from methyltriphenylphosphonium bromide (PPh 3 CH 3 Br), generated exo-methylene cyclohexane 18 in a very straightforward manner, and the product could be isolated by chromatography in 72% yield [17]. This olefin was then subject to a difluorocarbene cyclopropanation using TMSCF 3 and NaI, and this generated both isomers, 11a and 11b, in a ratio of 5:1, respectively.…”

“…Synthesis of compounds 11. Reagents and conditions: a) PPh 3 CH 3 Br, t-BuOK, diethyl ether, 0 °C to rt, 72%[17]; b) TMSCF 3 , NaI, THF, reflux; c) recrystallization, 27%.…”