4-Methyltetrahydro-1,4-oxazine-3,5-dione (5c). Reaction using diglycolic acid (6.7 g, 50 mmol) and a
40% solution of methylamine (4.2 g, 54 mmol) yielded the product (5.14 g, 80%) as colorless crystals which did
not require recrystallization; mp 72-74°C (lit. mp 78°C [5]); IR (nujol), , cm-1: 1732; m/z 129 (M+, 95%),
ν
100 (12), 71 (7), 44 (96), 42 (100).
4-Ethyltetrahydro-1,4-oxazine-3,5-dione (5d). Reaction using diglycolic acid (6.7 g, 50 mmol) and a
70% solution of ethylamine (3.54 g, 55 mmol) yielded the product (3.77 g, 53%) as colorless crystals from
acetonitrile; mp 29-30°C (lit. bp 95°C/15 Torr [5]). (Found, %: C 50.56; H 6.43; N 9.80. C6H9NO3.
Calculated, %: C 50.34; H 6.34; N 9.78). IR (thin film), , cm-1: 1742, 1685; m/z 143 (M+, 100%), 115 (15),
ν
85 (75), 56 (13), 42 (65).
4-Benzyltetrahydro-1,4-oxazine-3,5-dione (5e). Reaction using diglycolic acid (6.7 g, 50 mmol) and
benzylamine (5.4 g, 50 mmol) yielded the product (6.1 g, 60%) as colorless crystals wich did not require
recrystallization; mp 46-48°C (Found: m/z 205.0731 [M]+. C11H11NO3. Calculated: M = 205.0739); IR (melt),
, cm-1: 1780, 1740, 1682; m/z 205 (M+, 100%), 146 (60), 118 (22), 104 (40), 91 (51).
ν
4-Butyltetrahydro-1,4-oxazine-3,5-dione (5f). Reaction using diglycolic acid (6,7 g, 50 mmol) and
butylamine (5.11 g, 70 mmol) yielded the product (5.83 g, 68%) as colorless crystals from acetonitrile;
mp 26.5-27.5°C (lit. bp 139°C/16 Torr [5]). (Found: m/z 171.0891 [M]+. C8H13NO3. Calculated: M = 171.0895);
IR (thin film), , cm-1: 1750, 1670; m/z 171 (M+, 10%), 141 (56), 129 (10), 116 (70), 88 (40), 85 (52), 42 (100).
ν
Tetrahydro-1,4-thiazine-3,5-dione (6a). Reaction using thiodiglycolic acid (15 g, 100 mmol) and
aqueous ammonia (d 0.88, 15 cm3) gave the product (9.3 g, 71%) as colorless crystals which did not require
recrystallization; mp 118-120°C (lit. mp 128°C [3]); IR (nujol), , cm-1: 3420, 1728, 1270, 1194, 1143, 918,
ν
856, 790, 657.
4-Phenyltetrahydro-1,4-thiazine-3,5-dione (6b). Reaction using thiodiglycolic acid (4.6 g, 31 mmol)
and aniline (3.3 g, 35 mmol) with the normal procedure gave a solid after Kugelrohr distillation which consisted
partly of the non-cyclized thiodiglycolic acid monoanilide. This was heated with acetyl chloride (5 cm3) and
distilled until no more liquid came off. The residual solid was then Kugelrohr distilled to give the final product
(1.96 g, 31%) as pale orange crystals from acetonitrile; mp 214.5-215.5°C. Found, %: C 58.09; H 4.55; N 6.75.
C10H9NO2S. Calculated, %: C 57.95; H 4.38; N 6.76. IR (nujol), , cm-1: 1720, 1676; m/z 207 (M+, 100%).
ν
179 (17), 135 (8), 117 (27), 106 (18), 93 (19), 77 (17).
4-Methyltetrahydro-1,4-thiazine-3,5-dione (6c). Reaction using thiodiglycolic acid (7.5 g, 50 mmol)
and a 40% solution of methylamine (4.26 g, 55 mmol) yielded the product (3.72 g, 51%) as yellow crystals
which did not require recrystallization; mp 52-53°C. Found: m/z 145.0202 [M]+. C5H7NO2S.
Calculated: M = 145.0197. IR (melt), , cm-1: 1686; m/z 145 (M+, 100%), 88 (19), 84 (7), 60 (73).
ν
4-Ethyltetrahydro-1,4-thiazine-3,5-dione (6d). Reaction using thiodiglycolic acid (7.5 g, 50 mmol)
and a 70% solution of ethylamine (3.2 g, 50 mmol) yielded the product (3.85 g, 45%) as pale brown oily crystals
from acetonitrile; mp 29-31°C. Found: m/z 159.0350 [M]+. C6H9NO2S. Calculated: M = 159.0354. IR (thin
film), , cm-1: 1720, 1665; m/z 159 (M+, 9 %), 132 (28), 104 (20), 87 (100), 60 (55).
ν
4-Benzyltetrahydro-1,4-thiazine-3,5-dione (6e). Reaction using thiodiglycolic acid (7.5 g, 50 mmol)
and benzylamine (5.4 g, 50 mmol) yielded the product (8.2 g, 74%) as a colorless viscous liquid (Found:
m/z 221.0504 [M]+. C11H11NO2S. Calculated: M = 221.0511); IR (thin film), , cm-1: 1750, 1700; m/z 221
ν
(M+, 100%), 179 (16), 146 (45), 132 (76), 104 (40), 91 (85).
Flash Vacuum Pyrolysis of Tetrahydro-1,4-oxa(thia)zine-3,5-diones. General Procedure. The
sample was volatilized from a tube in a Büchi Kugelrohr oven through a 30 × 2.5 cm horizontal fused quartz
tube. This was heated externally by a Carbolite Eurotherm tube furnace MTF-12/38A at a temperature of 700°C,
the temperature being monitored by a Pt / Pt-13%Rh thermocouple situated at the center of the furnace. The
products were collected in a U-shaped trap cooled in liquid nitrogen. The whole system was maintained at a
pressure of 10-2 Torr by an Edwards Model E2M5 high capacity rotary oil pump, the pressure being measured
by a Pirani gauge situated between the cold trap and the pump. Under these conditions the contact time in the
hot zone was estimated to be ~10 ms.
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